Continuing to write to a large ROOT binary after it recovers from being closed improperly

ROOT
3

Again referring to this previous topic, I’m now trying something like this:

TFile recoverFullSumFile(fullSumPath, "update");
recoverFullSumFile.Write();
recoverFullSumFile.Close();

TFile fullSumFile(fullSumPath, "update");

TTree * fullSumTree = 0;
summaryClass * fullSum = 0;
unsigned int entryCount;

if (!fullSumFile.GetNkeys()) {

    fullSumTree = new TTree("treeName", "treeName");
    fullSumTree -> SetAutoSave(377625 / 10);
    fullSumTree -> Branch("summary", & fullSum);

    entryCount = 0;

} else {

    fullSumTree = (TTree *) fullSumFile.Get("treeName");
    fullSumTree -> SetBranchAddress("summary", & fullSum);

    entryCount = fullSumTree -> GetEntries();
}

I think this should work. But if not, why? Calling the same file twice like this, should I replace recoverFullSumFile.Close() with recoverFullSumFile.Close("R")?