Why does my iMac EMC number not match?

Hi everyone. I’ve got a 21.5” (late 2013) iMac sitting in front of me and I’d like to replace the machine’s hard drive with an SSD. The iMac is model A1418 with a 3.1GHz Intel i7 with NVIDIA GeForce GT 750M video card.

I’ve identified the machine on everymac.com using its serial number and there are three to choose from. The specs point at it being the most powerful machine of the three.

As a final check, I compared the EMC number of my machine (shown on the bottom of the iMac’s stand) and it says 2638. Eh? The only Apple model that matches that EMC number is the 2.7GHz i5. I was expecting to see 2742.

Does anyone know why this might be? I’m just being cautious that I’ve identified the exact model before opening her up! The specs check out, but the EMC number anomaly has confused me. Apple don’t make mistakes, do they?!!

Thanks.