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::OBJ, "error", /*ue, "",
                            {
                                {RPCResult::Type::ELISION, "", "JSONRPC error"},
                            }},
                        }},
                    }
                },
                RPCExamples{
                    HelpExampleCli("importmulti", "'[{ \"scriptPubKey\": { \"address\": \"<my address>\" }, \"timestamp\":1455191478 }, "
                                          "{ \"scriptPubKey\": { \"address\": \"<my 2nd address>\" }, \"label\": \"example 2\", \"timestamp\": 1455191480 }]'") +
                    HelpExampleCli("importmulti", "'[{ \"scriptPubKey\": { \"address\": \"<my address>\" }, \"timestamp\":1455191478 }]' '{ \"rescan\": false}'")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& mainRequest) -> UniValue
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(mainRequest);
    if (!pwallet) return UniValue::VNULL;
    CWallet& wallet{*pwallet};
    // 
    // 
    wallet.BlockUntilSyncedToCurrentChain();
    EnsureLegacyScriptPubKeyMan(*pwallet, true);
    const UniValue& requests = mainRequest.params[0];
    //
    bool fRescan = true;
    if (!mainRequest.params[1].isNull()) {
        const UniValue& options = mainRequest.params[1];
        if (options.exists("rescan")) {
            fRescan = options["rescan"].get_bool();
        }