In Gen 1, Magnemite and Magneton can be poisoned due to steel type not existing. In Gen 2 it is impossible for them to be poisoned because they gain the steel type, which is immune to poison. I also know that you can trade poisoned Pokemon from Gen 1 to 2 too. Basically my question is if you trade a poisoned Magnemite or Magneton that is poisoned in Gen 1 to Gen 2, would it still be poisoned?
Yes. Magnemite will still remain poisoned, as a GSC Magnemite can be poisoned using Twineedle.
Source: I asked this in Bulbapedia's Discord server and SadisticMystic answered it.