The Vincent 1991 memorandum was sent to MLB clubs and effectively was a CYA memo on Vincent's part to put the problem in the laps of the club owners and GM's.
I will not pretend to crawl into the mind of Fay Vincent and interpret his motivation beyond the basic observation above; but his current advice to Bud Selig on the Bonds HR record chase betrays him as both an "ego" and a gamesman. His advice to Selig to stay away for Bonds' #756 because of how his presence will "play" to the fans betrays more about him than any conjecture I might make.
Earlier, in 1986 I believe, Peter Ueberroth addressed substance abuse; and I believe that in the '90s, he would have handled the issue, negotiations and program implementation far more deftly and forcefully than either Selig or Vincent. Then too, there was the strike - a major distraction for any Commissioner.
In sending a memorandum to clubs, Vincent betrayed the figurehead nature of his own office and invited a number of interpretations and enforcement clarity as diverse as the number of franchises. It was a noble gesture, lacking authority and impact.
In a climate of misdirection, pro athletes will find the edge; UNTIL some AUTHORITY ENFORCES PROHITIBITIVE RULES.
That did not happen until after 2002, and even the, with no force until 2005.
From this link of Latin maxims:
qui nescit dissimulare nescit regnare and illegitimi non carborundum
"Laws come to the aid of those who are vigilant and not those who sleep."