So after a lot of Googling and searching I think I finally have an answer and it's all due to the standards set in the "Unicode CLDR Project"

It may be very new to us who are suddenly subjected to Windows 11 24H2, but in fact this standard has been around for years. If you go googling for "September changed from Sep to Sept" you will find people coming up against this issue for years on many different platforms. I found one such complaint dating back to 2015 and who knows there may be earlier ones.

Long story short: With regard to this standard, Microsoft is actually "late to the party". Others implemented it a LONG time ago.

All we can do is ask our clients to delay applying Windows 11 24H2 until we get around to fixing our software so it can handle this properly. Thankfully this turned out to be not as big a deal as I feared.

My apologies to anyone who came here hoping to find a "fix" but the only thing I can do is provide the answer to the question as stated. This is why it happened. We have to learn to live with it.