Just FTF is not enough, since people write things like "Missed the FTF by five minutes" all the time without actually being FTF.
There are a few combinations of smilies and "FTF" that do trigger detection of a log being an FTF without being a supported FTF tag, but they are exactly that: unsupported. To be sure, use one of the tags listed in the FAQ. Also note that you don't need to edit all your old logs. You can also create a public bookmark list with all your FTFs that don't have an FTF tag in the log and then specify that bookmark list as your FTF bookmark list in your profile on Project-GC (combining the FTF bookmark list and FTF tags is no problem).