Part 23 aircraft which have reverse generally provide charts for stopping with and without reverse or correction factors for it's use. Part 25 aircraft don't use reverse as part of the stopping equation.
If you're in a Part 23 airplane, how you use what's available to you is up to you.
Personally, I'd calculate it without reverse. You'll have only an advantage to contend with when it's available, and nothing to lose if it's not. If you plan to have reverse and then it's not available, you're plum out of luck.
Yes, that is what I believe. We do have performance charts including the help of reverser. But when I am going to calculate with that, I want to be shure that it is legal under JAR-OPS.
Inbalance