Well, here goes a long brain dump.
There is no objective score for pool, so it's not possible to use that as a baseline for "who is better." For example, the 100m freestyle swim is always 100m. So it's easy to see who is fastest across time. It's fairly objective to say that the best a decade ago was 10 seconds slower than today.
Fargo is a relative rating systems. You "earn" a rating relative to your contemporaries. It's a statistical analysis that I think has some inherent issues, but, overall, it is very good. Undoubtedly the best we've every had.
Consider: Shane in 2015 was the highest rated player at 824 Fargo. Now, he's a 846. And Filler is 860 today. So, a decade ago, would "best in the world" Shane be better or worse than today's #6 Shane, who is 20 points higher rated. And, how would 2015 Shane [best in the world then] compare to today's Filler [best in the world now]. Similarly, is Shane in 2015 (824) the same Fargo "caliber" player as Niels, Capito or Alcaide of today (~820). Fargo across time is weird.
Also, there is no cap for Fargo (as far as I know). And it looks like there has been some inherent inflation of the ratings (Fargo creep, which I think folks disagree with despite the top ranking increase over the last 10 years). That is (rhetorically), why is the best in the world today ago 40 points higher than the best in the world a decade ago? If this could be interpreted as a trendline, then we might see a 40 point drop every decade. This is odd to contemplate because, using this trend, 100 years ago the best-in-the-world would be a ~500 Fargo. While that seems low against today's numbers, against their peers in that era, if 500 was the highest rating you could get, then a 490 would still be world class.
Synthesizing that gibberish, one answer is that there would be no 800 Fargo rated players in the 70s or 80s because 800 Fargo didn't come to be until the middle 2000s and 850 didn't exist until recently. That is, even Shane (or whoever was #1 in 2000) might not even be 800. This isn't a perfect analysis, but you get the idea of one perspective on top Fargo over time.
But maybe you could apply some scaling factor to players in prior eras to put those players in ranked order and then say the top [then] would be 850 [now]. You could get a mapping using today's Fargo numbers, but it would just be for show with little statistical accuracy.
[note: I'm pretty sure Mike discussed using 1000 as a theoretical reference point for someone that is superhumanly dominant along the way. And I think 500 is the anchor point for average pool players. So the middle should stay the middle, but the top might continue to grow. Also, you can't really take the past data of players and insert it into the Fargo db and calculate scores because there would likely be too much statistical error. The number of datapoints would also be very small compared to what we have today].
-td [my two cents. Definitely worth much less]