I just noticed that my second M&P45 full size (serial HUK = 2014) doesn't have "Stainless" roll marked on the left side of the slide like my older one (serial DUK = 2010).
The roll markings are also noticeably more shallow.
The overtravel hump is also literally half the size of the older one.
I also noticed the serial on the newer one has the square scan code thing next to it. Just for curiosity sake, when did that start, and is it like those QR square codes that can be scanned with cell phones?

I know the machines in manufacturing wear down as production goes on, but I'm curious if this is correlated to any discernible decrease in quality of the firearm if it is a later model if wear parts in manufacturing haven't been replaced.

I know it's purely cosmetic as far as roll mark depth and how my two slides don't look alike with the missing "stainless" wording, but if you all haven't gathered from my posts, I'm a bit over-analytical/OCD about stupid stuff.

It's no difference.

The "QR code" is just an inventory control thing. Sig started putting them on stickers on specific models like the M11-A1.

From searching a bit, it seems like "Stainless" was dropped in 2011. Not to worry, the slides still are.