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 
{RPCResult::Type::NUM, "confirmations", "The number of confirmations of the most recent transaction included"},
                            {RPCResult::Type::STR, "label", "The label of the receiving address. The default label is \"\""},
                            {RPCResult::Type::ARR, "txids", "",
                            {
                                {RPCResult::Type::STR_HEX, "txid", "The ids of transactions received with the address"},
                            }},
                        }},
                    }
                },
                RPCExamples{
                    HelpExampleCli("listreceivedbyaddress", "")
            + HelpExampleCli("listreceivedbyaddress", "6 true")
            + HelpExampleCli("listreceivedbyaddress", "6 true true \"\" true")
            + HelpExampleRpc("listreceivedbyaddress", "6, true, true")
            + HelpExampleRpc("listreceivedbyaddress", "6, true, true, \"" + EXAMPLE_ADDRESS[0] + "\", true")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    const std::shared_ptr<const CWallet> pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return UniValue::VNULL;
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    const bool include_immature_coinbase{request.params[4].isNull() ? false : request.params[4].get_bool()};
    LOCK(pwallet->cs_wallet);
    return ListReceived(*pwallet, request.params, false, include_immature_coinbase);
},
    };
}
RPCHelpMan listreceivedbylabel()