It highlights a critical aspect of how transactions are validated, pointing out that a transaction's validation depends on the presence of its previous output (prevout) in the system. This requirement introduces a form of partial ordering, as it necessitates that the previous output must have been downloaded and available before the current transaction can be successfully checked. This condition underlines a fundamental constraint in the process of populating a Unspent Transaction Output (UTXO) store, which is crucial for maintaining the state of blockchain transactions.

Moreover, the discussion clarifies that this partial ordering requirement does not extend to necessitating a total ordering by block, which would imply a stricter sequence of operations. Instead, the focus is on the necessity for having access to prior transaction outputs to fulfill validation criteria, thereby allowing some flexibility in the order of transactions as long as the prerequisite conditions are met. This nuanced understanding of transaction dependencies and ordering requirements sheds light on the complexities involved in efficiently managing and verifying blockchain transactions, particularly in the construction and maintenance of the UTXO store, which is vital for the blockchain's operational integrity.