Not sure if this is going to help you..
This should give you some idea about the modification history of the drawing (save time etc.)
Frankly speaking i have never used it myself so please do test it .
If you have access to your license server log files, and know which dates/times you were working on this customers drawing(s) (vs. other customer drawings), you should be able to track the usage of the "drafting" license:
"a la carte" licensing:
23:47:18 (ugslmd) OUT: "drafting" USERNAME@HOSTNAME
23:51:29 (ugslmd) IN: "drafting" USERNAME@HOSTNAME
23:51:40 (ugslmd) OUT: "NX11110_drafting" USERNAME@HOSTNAME
0:11:59 (ugslmd) IN: "NX11110_drafting" USERNAME@HOSTNAME
There have been posts (maybe on lthe legacy BBS groups?) with "freeware" to parse the flex log file to get reporting, which may help you...
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled