It seems that it would otherwise silently skip the rescan for pre-backup used keys that are still waiting to be generated into the keypool?

See also #11249 
{
    return{{RPCResult::Type::NUM, "confirmations", "The number of confirmations for the transaction. Negative confirmations means the\n"
               "transaction conflicted that many blocks ago."},
           {RPCResult::Type::BOOL, "generated", true, "Only present if the transaction's only input is a coinbase one."},
           {RPCResult::Type::BOOL, "trusted", true, "Whether we consider the transaction to be trusted and safe to spend from.\n"
                "Only present when the transaction has 0 confirmations (or negative confirmations, if conflicted)."},
           {RPCResult::Type::STR_HEX, "blockhash", true, "The block hash containing the transaction."},
           {RPCResult::Type::NUM, "blockheight", true, "The block height containing the transaction."},
           {RPCResult::Type::NUM, "blockindex", true, "The index of the transaction in the block that includes it."},
           {RPCResult::Type::NUM_TIME, "blocktime", true, "The block time expressed in " + UNIX_EPOCH_TIME + "."},
           {RPCResult::Type::STR_HEX, "txid", "The transaction id."},
           {RPCResult::Type::STR_HEX, "wtxid", "The hash of serialized transaction, including witness data."},
           {RPCResult::Type::ARR, "walletconflicts", "Conflicting transaction ids.",
           {
               {RPCResult::Type::STR_HEX, "txid", "The transaction id."},
           }},
           {RPCResult::Type::STR_HEX, "replaced_by_txid", true, "The txid if this tx was replaced."},
           {RPCResult::Type::STR_HEX, "replaces_txid", true, "The txid if the tx replaces one."},
           {RPCResult::Type::STR, "to", true, "If a comment to is associated with the transaction."},
           {RPCResult::Type::NUM_TIME, "time", "The transaction time expressed in " + UNIX_EPOCH_TIME + "."},
           {RPCResult::Type::NUM_TIME, "timereceived", "The time received expressed in " + UNIX_EPOCH_TIME + "."},
           {RPCResult::Type::STR, "comment", true, "If a comment is associated with the transaction, only present if not empty."},
           {RPCResult::Type::STR, "bip125-replaceable", "(\"yes|no|unknown\") Whether this transaction signals BIP125 replaceability or has an unconfirmed ancestor signaling BIP125 replaceability.\n"
               "May be unknown for unconfirmed transactions not in the mempool because their unconfirmed ancestors are unknown."},
           {RPCResult::Type::ARR, "parent_descs", true, "Only if 'category' is 'received'. List of parent descriptors for the scriptPubKey of this coin.", {
               {RPCResult::Type::STR, "desc", "The descriptor string."},
           }},
           };
}
RPCHelpMan listtransactions()