I think this might be a flawed approach of looking at things. Other examples might be golf, chess, and StarCraft.
Golf:
It's easy to say Tiger Woods is the greatest player of all time, but realistically speaking, who would win in a match: Tiger in his prime, or Jack Nicklaus in his prime? No one knows the answer, because technology has changed so much in the sport that competition has been forced to evolve.
Chess:
It's easy to say Bobby Fischer is the greatest player of all time, but realistically speaking, who would win in a match: Fischer in his prime, or Kasparov in his prime? It's hard to say, because with modern computer analysis Kasparov could easily and quickly analyze every tournament game Fischer had ever played and create strategies to specifically deal with him. Fischer in his prime did not have the luxury of computer analysis.
StarCraft:
For a long time, the OSL was the most prestigious StarCraft tournament. What would happen if the winner of the 2004 OSL faced the winner of the 2010 OSL? Even though they were on the same skill level, the 2010 OSL champion would win simply due to the game being more figured out at the time of his prime.
The Point:
If time travelers visited the early 80's and delivered to Billy and Steve a video of Dean's 1.2m game, what would their PBs be today? I would venture to guess their PBs would be much higher. I would also venture to guess this applies for any competitive 80's game.
Complex games take years to figure out, and skill often goes through generations of players. Each generation figures out something new and masters what came before it.