[Topnotchsy]

I'm not a true expert, but own many Jackie signatures and have learned a few things over the years. The Jackie looks a little unusual to me but there are two reasons I would be surprised if it was a clubhouse sig:

1) In general, unless a ball was 100% signed clubhouse, it would be passed around the team to be signed firt and only then filled in by people in the clubhouse. Because of this (in my experience), if you find a clubhouse signature, you will generally find the signatures underneath it are also clubhouse signatures since they would start after the players finished. It is possible that Jackie had not signed and there were no other spots left to sign so a clubhouse attendant signed on the Spalding logo, but I doubt it.)

2) Generally, clubhouse signatures are all the same color since they were using a single pen. This ball is signed with many different pens, and Jackie's is signed with a black pen. Given this reality, I am quite confident that a clubhouse attendant was not signing the whole panel