Realm linear migration of removed Object

Question

I am facing a migration of a Realm backed object for a large and long running app. The object has gone through several property migrations in its lifespan and has recently been removed from the app altogether.

As Realm migrations happen in a linear approach from oldest to newest schema version I understand a user coming from several versions old app will migrate through all versions one by one before reaching the latest. This has never been in issue in the past, I'm just wondering what approach is needed when now that object will no longer exist in the latest version, so previous migration class references cannot be found.

A simplified example.

V1 schema

class Customer: Object {
    @objc dynamic var customerId: String?
    @objc dynamic var surname: String?
    @objc dynamic var givenName: String?
}

V5 schema

class Customer: Object {
    @objc dynamic var customerId: String?
    @objc dynamic var surname: String?
    @objc dynamic var givenName: String?
    @objc dynamic var fullName: String?
}

V16 schema

class Customer: Object {
    @objc dynamic var customerId: String?
    @objc dynamic var surname: String?
    @objc dynamic var givenName: String?
    @objc dynamic var fullName: String?
    @objc dynamic var lastVisited: Date?
}

V20 schema

//Customer object does not exist anymore

Example migration through schema versions

migrationBlock: { migration, oldSchemaVersion in
    if (oldSchemaVersion < 5) {
        migration.enumerateObjects(ofType: Customer.className()) { oldObject, newObject in
            let givenName = oldObject!["givenName"] as! String
            let surname = oldObject!["surname"] as! String
            newObject!["fullName"] = "\(givenName) \(surname)"
        }
    }

    if (oldSchemaVersion < 16) {
        migration.enumerateObjects(ofType: Customer.className()) { oldObject, newObject in
            if let newObject = newObject {
              newObject["lastVisited"] = Date()
            }
        }
    }

    if (oldSchemaVersion < 20) {
      //I want to delete all Customer data for an object that no longer exists
    }
}

My issues now are:

1. Build errors will exist on the migration lines with enumerateObjects(ofType: Customer.className()) as Customer does not exist anymore.

2. The properties being migrated in v5 and v16, and all the other Customer properties do not exist anymore. Does this matter?

3. I want to delete all data in v20 and remove the Customer object.

My thoughts:

1. Do I go back and modify older previous migrations to instead use the string name instead of className? eg.

enumerateObjects(ofType: "Customer")

2. Given that I no longer care about the customer properties in earlier migrations and any user updating will end on V20 is the final migration as simple as:

migration.deleteData(forType: "Customer").

3. What will be the experience for a user moving from v5 -> v20?