Model number On the back case “A1954” in Settings: “MR752LL/A”. Why two different “Model” numbers?

A1954 is the model number and identifies it as an iPad (6th generation) Wi-Fi + Cellular. MR752LL/A is an Apple part number and more specifically identifies it as Space Gray, 128 GB, US and Canada (the "LL" part is a region code).

A1954 is the model number for an iPad 9.7” 6th generation (Wi-Fi/cellular).

MR752LL/A is Apple’s order number.

In Settings, if you tap the MR7252LL/A field, it will switch to the generic “A” model identifier - A1954.

The full model number encodes additional information, that includes the device colour, storage configuration, manufacturing details etc.