Here is the "experts" information on which F1TDC config file is being used in this run:
[cdaq@cdaql4 f1tdc_config_files]$ ls -la current.dat lrwxrwxrwx 1 cdaq c-cdaq 29 Jul 14 2010 current.dat -> r2_r116ps_w1500ns_l1600ns.dat
Note that the last time these parameters were changed appeared to be July 14, 2010. There is a log entry that day from John Leckey indicating that they were changed to these values. I did a cosmic run after that date (run 759 on July 25, 2010) that showed that there was still at least ~ 80 nsec prior to "t=" in the drift time distribution. So whatever caused the apparent cutoff we have in the Run I data must have been something else; like a shift in the trigger signal somehow. I'll have to hunt for that later; right now I'm just trying to confirm the apparent cutoff by using our existing window width and then a very wide one in the next run.