In the early 90's Castrol TXT 10W40, they called it a semi-synthetic back then, but I think by today's standards it would be called a full synthetic. I think it contained an early Group 3 which I believe Castrol called semi-synthetic back then. Maybe it was a Group 3 & Group 4 blend, if any Castrol people from back in the day can confirm, I would love to know. It was great stuff, rated CCMC European Test Sequences G4, G5 and PD2, which pre-dates the ACEA specs. It lasted better in my shared sump motorcycles than the heavier GTX 20W50, which was quickly chewed up by the gear box & engine combination.
In the mid 90's, when they stopped selling TXT, I moved to Castrol Formula-R 10W-60 full synthetic, their PAO based performance blend. In the mid to late 2000's they renamed this Castrol Edge 10W60.