A couple of Questions.
1. When set to special to the high scores receive a credit?
2. Does it happen for all players, or only some?

If it scores credits but not free balls then the issue is Y-B-5 near e17/e7 on the schematic. Check for continuity, especially around the jones plugs.
If it doesn't score credits, or works for some players and not others then I would look at the player unit and score reels.

My Argosy is set up for free play and it still adds credits on high score, when special is lit and end of game matches.

Do you get a credit for Playfield specials?

congrats.