Ok, to answer my own question: it is IMPOSSIBLE to check too much.
Checked LH572 before I went to bed at 11pm EDT, got an x.
Checked LH572 this morning at 10am EDT, got a big ole O! ^
Or maybe LH keeps an eye on this forum and were testing me to see how long it would take me to find it after I posted my travel date here.
In any case, it's 747 row 83 on all the flights now, so unless I can mix in some LX to break up the 15 hours in FRA I feel pretty good. ^