In regards to return data type. A field like subsidiary is classified as a number in the debugger but it's really a String. I assume if a field value is an internal ID, this would always be a number and not a string? Or is the result of getValue for that type of field always a String too?

I think getValue always returns a string. The string though is the Internal ID of that record (in this case, Sub). Simply cast to a number

I can see a lot of code in an old module that assumes the return type is an int