And it was supposed to be a one-time amnesty.
I never said it wasn't. I said that Reagan called it "legalization", not amnesty as you posted. And yes, it was meant to be a one time deal.
The more relevant point which you ignored entirely, was Fat Teddy gutting the IRCA of 1986 of its enforcement and sanction funding. This turned a limited grant of amnesty to an original estimate of some 300K into a blanket amnesty. A policy that continues to drive the open borders crowd till this day.
Reagan never envisioned the IRCA of 1986 as a blanket amnesty. Period.