Bob, while the 1988 rules were the first where the R&A stated that the ball would be 1.68 inches, they also said that the small ball could be played until December 31, 1989, so 1990 was the first time that everyone was required to play the larger ball.
The following notes were in the 1988 rules:
"1. The size specified in (b) above will take effect from 1st January 1990. Until that date the previous size specification of a diameter not less than 1.620 inches (41.15mm) will apply.
2. The Overall Distance Standard will apply only to balls which meet the new size specification of a diameter not less than 1.680 inches (42.67mm).
3. In international team competitions, until 31st December, 1989, the previous size specification of a diameter not less than 1.620 inches (41.15mm) will apply."
You are right that the 1.68 ball is easier to hit off the ground than the 1.62. If you read my opinion piece you will see that the reason the USGA kept the 1.68 size when they went back to the 1.62 ounce weight was for that reason. Players liked the size, they hated the light weight of the balloon ball.
I loved going to England when I was young and getting some of the individually wrapped balls. I wish I still had some.