Why am I getting unresolved external symbol when trying to use sgp4 with this CMakeLists.txt?

Question

I am trying to write a simple test executable that links with the SGP4 library. However, I believe there is something wrong with how I've written my CMakeLists.txt. Configuration goes off without a hitch. However I get LNK2019: Unresolved external symbol... errors during the build step.

I have used target_link_libraries to point at each and every .lib file, and target_include_directories to point at the associated header files. There must be an additional step, or mistake I've made somewhere. What am I missing?

This is the file structure of my project:

sgp4_sandbox
├───test.cpp
├───CMakeLists.txt
├───build
└───Sgp4Prop
    ├───Documentation
    ├───Lib
    │   └───Windows          <-------------------- .lib and DLLs here
    ├───SampleCode
    │   └───C
    │       ├───DriverExamples
    │       │   ├───OscVecToTLE
    │       │   ├───services  <------------------- HEADER FILES HERE
    │       │   ├───Sgp4Prop  
    │       │   ├───Sgp4Prop_Simple
    │       │   ├───ShowVersion
    │       │   ├───TleReepoch
    │       │   └───wrappers  <------------------- HEADER FILES HERE
    │       └───x64
    │           └───Debug
    ├───UnitTests
    ├───Utilities
    └───Verify

Here is my CMakeLists.txt:

cmake_minimum_required(VERSION 3.10)

project(SGP4_sandbox
    VERSION 0.1
    DESCRIPTION "Sample project to play with sgp4"
    LANGUAGES CXX
)

add_executable(test test.cpp)

set(SGP4_LIB_PATH "${CMAKE_CURRENT_SOURCE_DIR}/Sgp4Prop/Lib/Windows")

target_include_directories(test 
    PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/Sgp4Prop/SampleCode/C/DriverExamples/wrappers"
    PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/Sgp4Prop/SampleCode/C/DriverExamples/services")

target_link_libraries(test 
    PRIVATE ${SGP4_LIB_PATH}/AstroFunc.lib
    PRIVATE ${SGP4_LIB_PATH}/DllMain.lib
    PRIVATE ${SGP4_LIB_PATH}/ElOps.lib
    PRIVATE ${SGP4_LIB_PATH}/EnvConst.lib
    PRIVATE ${SGP4_LIB_PATH}/ExtEphem.lib
    PRIVATE ${SGP4_LIB_PATH}/Obs.lib
    PRIVATE ${SGP4_LIB_PATH}/SatState.lib
    PRIVATE ${SGP4_LIB_PATH}/Sensor.lib
    PRIVATE ${SGP4_LIB_PATH}/Sgp4prop.lib
    PRIVATE ${SGP4_LIB_PATH}/SpVec.lib
    PRIVATE ${SGP4_LIB_PATH}/TimeFunc.lib
    PRIVATE ${SGP4_LIB_PATH}/Tle.lib
    PRIVATE ${SGP4_LIB_PATH}/Vcm.lib)

My simple test.cpp, largely copied from some demo code:

#include <iostream>

// Compiler directive that allows C++ code to use the C header files
// Begin
#ifdef __cplusplus
extern "C"
{
#endif

#include <DllMainDll_Service.h>
#include <TimeFuncDll_Service.h>
#include <DllMainDll.h>
#include <EnvConstDll.h>
#include <AstroFuncDll.h>
#include <TimeFuncDll.h>
#include <TleDll.h>
#include <Sgp4PropDll.h>

// End compiler directive
#ifdef __cplusplus
}
#endif

// Forward declare loaders and free-ers 
void  LoadAstroStdDlls();
void  FreeAstroStdDlls();

int main() {

    LoadAstroStdDlls();
    FreeAstroStdDlls();
}

// Load all the dlls being used in the program
void LoadAstroStdDlls()
{
    // Load MainDll dll
    LoadDllMainDll();

    // Load EnvConst dll and assign function pointers
    LoadEnvConstDll();

    // Load TimeFunc dll and assign function pointers
    LoadTimeFuncDll();

    // Load AstroFunc dll and assign function pointers
    LoadAstroFuncDll();

    // Load TLE dll and assign function pointers
    LoadTleDll();

    // Load Sgp4Prop dll and assign function pointers
    LoadSgp4PropDll();
}


// Free all the dlls being used in the program
void FreeAstroStdDlls()
{
    // Free MainDll dll
    FreeDllMainDll();

    // Free EnvConst dll
    FreeEnvConstDll();

    // Free AstroFunc dll
    FreeAstroFuncDll();

    // Free TimeFunc dll
    FreeTimeFuncDll();

    // Free TLE dll
    FreeTleDll();

    // Free Sgp4Prop dll
    FreeSgp4PropDll();
}

And finally, here is the output of calling cmake --build .

CMake is re-running because C:/Users/E40056742/projects/SGP4_sandbox/build/CMakeFiles/generate.stamp is out-of-date.
  the file 'C:/Users/E40056742/projects/SGP4_sandbox/CMakeLists.txt'
  is newer than 'C:/Users/E40056742/projects/SGP4_sandbox/build/CMakeFiles/generate.stamp.depend'
  result='-1'
-- Selecting Windows SDK version 10.0.19041.0 to target Windows 10.0.19044.
-- Configuring done (0.0s)
-- Generating done (0.0s)
-- Build files have been written to: C:/Users/E40056742/projects/SGP4_sandbox/build
Microsoft (R) Build Engine version 16.11.2+f32259642 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

  Checking Build System
  Building Custom Rule C:/Users/E40056742/projects/SGP4_sandbox/CMakeLists.txt
test.obj : error LNK2019: unresolved external symbol FreeDllMainDll referenced in function "void __cdecl FreeAstroStdDlls(void)" (?FreeAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol LoadDllMainDll referenced in function "void __cdecl LoadAstroStdDlls(void)" (?LoadAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol LoadEnvConstDll referenced in function "void __cdecl LoadAstroStdDlls(void)" (?LoadAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol FreeEnvConstDll referenced in function "void __cdecl FreeAstroStdDlls(void)" (?FreeAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol LoadAstroFuncDll referenced in function "void __cdecl LoadAstroStdDlls(void)" (?LoadAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol FreeAstroFuncDll referenced in function "void __cdecl FreeAstroStdDlls(void)" (?FreeAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol LoadTimeFuncDll referenced in function "void __cdecl LoadAstroStdDlls(void)" (?LoadAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol FreeTimeFuncDll referenced in function "void __cdecl FreeAstroStdDlls(void)" (?FreeAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol LoadTleDll referenced in function "void __cdecl LoadAstroStdDlls(void)" (?LoadAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol FreeTleDll referenced in function "void __cdecl FreeAstroStdDlls(void)" (?FreeAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol LoadSgp4PropDll referenced in function "void __cdecl LoadAstroStdDlls(void)" (?LoadAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
test.obj : error LNK2019: unresolved external symbol FreeSgp4PropDll referenced in function "void __cdecl FreeAstroStdDlls(void)" (?FreeAstroStdDlls@@YAXXZ) [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]
C:\Users\E40056742\projects\SGP4_sandbox\build\Debug\test.exe : fatal error LNK1120: 12 unresolved externals [C:\Users\E40056742\projects\SGP4_sandbox\build\test.vcxproj]