of course - that wasn't the question you were asking. numbering restrictions have been a part of the game from the start - I don't really know when the current revision took effect. it's been in Canadian amateur since forever.
All I have been able to find is a 1968 NCAA rule
wherein a compulsory numbering system makes only players numbered other than 50-79 eligible forward pass receivers. The link is not an official NCAA link but it would seem to make sense
[url]David Wilson's Homepage
I couldn't find any similar rule histories involving the CFL, CIS, or NFL. But I think it would be safe to assume these changes would have been across the board, give or take a year or two.