As recently as the 1960s, pro bats (seen in museums) seem to have been marked 4 star.
Yip and the markings changed at about the same time as they became part of Slazenger. Most of the ones online I've seen for later years were autograph style bats, especially Huttons.
Been looking at old photos of batsmen trying to discern the bat markings but generally they are too grainy to tell. I'd imagine a lot of the top players were using Gradidges back then but doesn't seem that sponsorship was a big thing.
Have given it to Richard at Bear Bats to refurbish so will be fascinating to see how 100 year old willow plays. Though as the top grades were air dried for 30 years back then it's likely a lot older.