What sketchy documentation I do have says G10 is date setting.
If I write the value to G54 I loose the original number and won't be able to just have the operator enter his part stick out into #101. If I write to work shift I think it would accumulate if you reset and started the program from the top.
Again, the hope was that the operator could enter his part length or stick out in a parameter at the top of the program. New part, new #101 value and hit go.
Tom