After going through all of the inferences, we are left with a concrete order except for P.
N O R S M T ___ ___ ___ ___ ___ ___ ___ 89 90 91 92 93 94 95
The only remaining remaining variable is P. And it must be placed between N and M. Therefore in order to provide the "complete" list of those who can be between 89 and 91, we would have to include P.
I hope this helps. Please let me know if you have any other questions or would like me to elaborate further!