On another note: what I actually meant with my comment is that I'm kind of amazed Apple still has parts for a 2yr (and presumably 3yr according to OP) old laptop, since they usually push their old stock out pretty aggressively. They either must have giant warehouses full or still have the factories churning out old parts??
Much of this is legally required (and as well, they can get a higher price for new devices when the older ones hold their value). If you check the Apple web site you'll see that how far back they will fix your device varies by jurisdiction (country and even state): https://support.apple.com/en-us/HT201624
I assume largely they stock pile them in advance, be interesting to find out for sure how that works.