I bought a new 15" retina MBP earlier this year, with the discrete GPU M370X that was released this year. However, "About this Mac" claims that it's a Mid 2014 model. Is it just a glitch or does anyone else have the same info? It's nothing to worry about, right?
I'd be curious what you find by plugging the last 4 of the serial number into this script: https://apple.stackexchange.com/a/98089/5472 I've known cases where the serial number was encoded improperly and you'd need to collect your invoice/shipping document and contact the vendor or Apple to make sure you got the hardware for which you paid.
Apple does identify models by the year in which it was originally released. If you walk into an Apple Store and buy a Mac Pro that was made last week, you will still see that it's a 2013 model since they haven't updated that platform since then.
$ curl -s http://support-sp.apple.com/sp/product?cc=F693 | sed 's|.*<configCode>\(.*\)</configCode>.*|\1|' Mac Pro (Late 2013)
I would guess that you have nothing to worry about and that the marketing number wasn't bumped when your model specifications were upgraded. Especially since you are tracking the GPU, it's unlikely you have a wrong model. If you're really worried, get an
sysdiagnose and full system information dump to Apple Support and have them verify in writing that you were sold the proper model.
A visit to the genius bar (if convenient) might be the fastest way to have someone look up the service manual and check things since you wouldn't need to send any files in and could get an immediate answer.