Reagan's amnesty was a one time deal that failed. That wasn't predictable so he had no way of knowing. Perry had benefit of knowing but did it anyway because it was part of his pro-ILLEGAL agenda. There's a world of difference between the two men, their goals and their agendas.
The political outcome sure was predictable.
There are Hispanic polls that go all the way back to Nixon-Kennedy in 1960.
No Republican presidential candidate has ever received more than 40% of the Hispanic vote.
Reagan got 35% in 1980 and 37% in 1984.
After the Reagan Amnesty passed in 1986, GHWBush ran in 1988 and got 30% of the Hispanic vote!