Function nsm_subsidy_is_valid 

pub(crate) fn nsm_subsidy_is_valid(
    contextual: &ContextuallyVerifiedBlock,
    network: &Network,
    parent_chain_value_pools: ValueBalance<NonNegative>,
    block_miner_fees: Amount<NonNegative>,
) -> Result<(), ValidateContextError>

Checks the block subsidy, funding streams, and miner fees paid by contextual’s coinbase transaction, from the NSM reissuance height.

The block verifier checks the subsidy, funding streams and miner fees before the deployment height. From then on the block subsidy depends on the NSM value balance after the parent block, which is only known during contextual validation, so the checks run here instead.