OP, I have seen BIOSs from different cards in the same line from the same manufacture that have the exact same BIOS number on them and the same model cards that have different BIOS numbers on them.
 
It really makes no rhyme or reason for us consumers and only means something to the manufacture and team of engineers that come up with the BIOS of the card.
 
The EVGA tech is correct though that the different numbers would most likely be the different base and boost speeds the two cards have and possibly power limit and memory brand\timing differences.
 
Beyond that, the only way for us to know, would be to compare the two BIOSs side by side with a proper BIOS editing utility (which is not available to us consumers) as Nvidia has completely locked down the ability to edit the BIOS on Pascal & Turning based cards (this is why everyone is using different BIOSs from different cards/manufactures and flashing them to their cards (voids warranty of card) and why the EVGA tech makes the "It's recommended to not flash the BIOS on a graphics card unless we release a new BIOS for your exact card" statement).
 
Unless you know someone at Nvidia or in the graphics card manufacturing circles that has some pull, you would not have access to the software\hardware required to do this.