actually the PTR retinol fusion pm is a 1.5%. There is no limit that it can have in a product because it is not regulated my the FDA and it is not as strong as its prescription cousins of retinoids.
I use the ptr 1.5% retinol every night with zero irritation even from the very first night of appication on. i was able to start using it daily with no redness or peeling issues. and this is comming from someone who could NEVER use a retinol because i would get sick of the constant irritation. either try the PTR retinol or Miracle Worker pads from Philosophy.
Sephora carries several products including Peter Thomas Roth Retinol Fusion PM with has some nice ingredients (retinol, squalene, vit. C and E) but it doesn't list the actual percentage of retinol. There are retinol products on the market from 0.3 to 0.9 % but the highest I've seen is SkinCeuticals Retinol 1.0. I use it...it's wonderful and contains no parabens.
Hope that helps.