How to return tx to mempool from stale block?

Question

This question is centered around the implementation of how transactions from a reorganized block return to the mempool.

In my understanding, once a block becomes organized out of the best chain all its transactions (that aren't in blocks of the best chain) need to return to the mempool.

Do we start from genesis block until we reach the last block of the active chain checking every transaction along the way, or is it there a more efficient algorithm that's based on some constraint/property that allows the algorithm to start from a more recent block?

Proto code for starting from the genesis block:

Blockchain blockchain = ...
function Dictionary<Key, Tx> deleteOrphanTx (Dictionary<Key, Tx> orphanTx) {
    foreach (Block currBlock : blockchain.getBlocks())
        foreach (Tx tx : currBlock.getTx())
            Key txKey = tx.getKey();
            if(orphanTx.contains(txKey)
                orphanTx.remove(txKey);
    return orphanTx;
}

Answer 1

Proto code for returning transactions from orphan block:

foreach ( tx: orphanBlock )
  if ( tx.isValidAfterReorg ( ) )
    mempool.insert ( tx );

Answer 2

Since there weren't other entries and the only answer didn't provide a clear answer to my question, I'm going to sum up what I found to be the solution to my question.

There are no properties or constraints that allow the algorithm to start from a more recent block. In order to check if a transaction from an orphan block needs to go back to the mem pool, one needs to start from the genesis block and check every block along the way to guarantee that the transaction doesn't already belong to a validated block. If at the end no blockchain no block contains said transaction, we need to add it back to the mem pool.

If in the meantime someone participates with more relevant information I'll happily delete this answer.