No, not really.
Without going into excessive detail, each Cellular 850 MHz A/B block originally was 10 MHz FDD, later expanded in a necessarily convoluted way to 12.5 MHz FDD. But both origin and expansion were decades ago in the 1980s, long before the wireless iterations AT&T and VZW came into being. As such, the Cellular A/B blocks were not partitioned between AT&T and VZW. Rather, they were awarded in each market to an incumbent wireline provider and, in beauty contest fashion, to a new entrant.
Fast forward to recent times, Cellular A/B licensees include USCC, C Spire, Viaero, Commnet, et al., even T-Mobile in a single market, not just AT&T and VZW. In fact, AT&T, VZW, or both are shut out in a few markets, though AT&T and VZW do hold the vast majority nationwide of Cellular A/B licenses, and in some markets, either AT&T or VZW holds both Cellular A/B blocks.
AJ