DouglasLourey

Thanks marc, I really enjoyed reading your explanation; I was able to visualize it.  And I also appreciate the additional clarification points.
 
I'm a retired computer programmer and network guy, also pc support.  Not an engineer, more a mechanic.  More breadth and less depth, so analogies like yours are information I always remember; the finer points not so much.

The following article may be useful.  The link is elsewhere in this forum.
Midland 400 use 13 for DCS Code 073 and 39 for 265.
Hopefully, others will be able to explain this, but this may be a start.
 
https://www.k0tfu.org/reference/frs-gmrs-privacy-codes-demystified.html