Yes, with grass all bets are off and the perf data goes largely out of the window if you are looking for any accuracy.
For example a TB20 might be able to lift off in 400m on tarmac but with say 10cm grass it could be 600-800m. There are no formulae for this, nothing in the POH. With grass you just need really big margins. Most of the time people do have these, with say 700m+ runways, but sometimes they push it really close thinking grass is like tarmac, but it never will be. The best you will get is a really smooth ground and really short dry grass.
Add some upslope and the unknowns multiply.
