B12 is split into 3 6MHz FDD blocks, the A block (728-734/698-704), the B block (734-740/704-710) and the C block (740-746/710-716). If Appalachian is running a 10x10 B12 LTE carrier, that means they must own at least two blocks. The EARFCN, 5120, equates to center frequencies of 740/710 MHz, suggesting that they own the B and C blocks. This means only the A block is left over for either AT&T or T-Mobile, so in short, yes, Appalachian using B12 means less B12 for everyone else.