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 
status = DatabaseStatusFAILED_LOAD;
            return nullptr;
        }
        NotifyWalletLoaded(context, );
        AddWallet(context, );
        ->postInitProcess();
        
        UpdateWalletSetting(*context.chain, name, load_on_start, warnings);
        return ;
    } catch (const stdruntime_error& e) {
        error = Untranslated(e.what());
        status = DatabaseStatusFAILED_LOAD;
        return nullptr;
    }
}
class FastWalletRescanFilter
{
public
    FastWalletRescanFilter(const CWallet& )  m_()
    {
        // 
        assert(!m_.IsLegacy());
        // 
        for (auto spkm  m_.GetAllScriptPubKeyMans()) {
            auto desc_spkm{dynamic_cast<DescriptorScriptPubKeyMan*>(spkm)};
            assert(desc_spkm != nullptr);
            AddScriptPubKeys(desc_spkm);
            // 
            if (desc_spkm->IsHDEnabled()) {
                m_last_range_ends.emplace(desc_spkm->GetID(), desc_spkm->GetEndRange());