I have the same question. This has been posted on the Facebook forum.

The ball is equivalent. The source has been postulated as driving range supplied, used by instructors with students, to being used at pro events at the Tour driving ranges.

That it is stamped, like a Practice or X-out ball, likely means it isn’t valid for competition but you can expect the same performance. Beyond small cosmetic issues, I wouldn’t expect Titleist to sell a defective ball labeled as the flagship product.

The pros at our course gets balls from the rep that are stamped STAFF. Same ball as I play. Ball most likely was found in the ponds that they (lostballs.com) have contracts to dive and sold to the public in their mass quantities of golf balls. Pros loose balls like us as well. Enjoy you find.

Driving Range ball - couple of years ago, one of the marshalls on the range tossed a couple over to my son whilst we were at The Open. One ProV1 and one ProV1x. Both were marked Tour.

I saw these types of balls a few years ago at Firestone CC on the driving range. They most likely were left over from the Champions Tour event.