I think even if you call the initial self-publication of Ken St. Andre's game too narrowly distributed to count, it's less than 5 years between the publishing of the original books to when there were a number of different choices out there. Traveller was like 77 I think, Runequest was either 77 or 78. Villains and Vigilantes was out sometime in the 70s as well. I'm sure I'm probably missing some others. So we're talking at most 2-3 years, not a huge amount of time. Once the idea was out there lots of folks started seeing both the potential and the limits of what TSR was publishing and started making their own.