(Previously a process has been discussed with six different stages, so "previously-listed" refers to its third and fourth stage.) Tom.
Tom, your sentence says: A process has been discussed with six different stages.
(let's stop here.) What this statement says is, " An unknown actor discussed an unknown subject with a committee of six different stages"
So what were the stages' comments about the process?
Maybe you mean to say, "A process with six different stages has been discussed WITH WHOM? WHEN, WHERE, WHY?
Your sentence is lacking fundamental elements to be a complete sentence: you need to add, or shift around, some syntactic elements into the pile. Then organize according to the simplest formula there is:
English Sentence - Subj (NP)+ VP + Obj (complement of clauses that is where WHO, WHEN, WHY are stringed)