Allow Player Competition was added to Whitestar around April 26, 2003, as that is when the TSPP readme says it got added to the code (v3.00). It was based on the Williams games that did it in the 90s starting somewhere around JackBot (I don’t remember exactly when). It’s listed in LOTR’s manual, so it should’ve been standard on games released in 2003 and beyond.
I don’t remember when it got added to SAM, but it was probably a day 1 feature.