Snowflake Dynamic Table support for`UNION ALL`

Question

While trying to modify an existing table to be a Dynamic table, I noticed that it was not incrementally refreshing like I had hoped. refresh_mode_reason is given as below.

Change tracking is not supported on queries with UNION ALLs or outer joins that would produce conflicting ROW_IDs.

However, within the table in Understanding dynamic table refresh: Types of queries that support incremental refreshes it says:

Dynamic tables support UNION ALL.

theories

1. Behind-the-scenes Snowflake determines whether the UNION ALL results in "conflicting ROW_IDs, if so, only full refresh is supported
2. the docs are misleading and should really say: "Dynamic tables support UNION ALL, but not incremental refresh"
3. Or is this a bug with dynamic tables?

related questions

Dynamic tables with UNION -- change tracking not enabled