Yep, my bad. Of course, you are right. Usually SC doesn’t show you stuff that’s not relevant, but given a form has multiple ways of working, that makes sense (I just jumped in and saw it was there - d’oh!)
The reason onLoad won’t work is still a valid point as that is triggered by the loading of the app itself. By copying a record the app is not reloaded, just a record is loaded (hence suggesting onRecord).
onNavigate may get triggered by the copy. Might want to try in there perhaps (not tested this). If you do (and it works) use the sc_btn_copy macro mentioned before to test, as I presume you only want the pre-fill to occur after a copy, not every time you move to a different record (assuming you have navigation options on)