reuse plastic pellets

I am new here also, and very green on rock tumbling, but I have read that you should change the plastic pellets every time you change grit, and especially for 400, pre-polish and polish stages. Don't throw the old pellets, just keep them seperated and marked for which grit you used them for and you can reuse them. I have learned that it probably isn't necessary to use them for the first tumble unless you have very soft material (rocks).
Others in here will surely give you the straight scoop on this and are most helpful.

i have been using the same pellets for months in the same size grit or polish .
some times if i feel that they have been used long enough in onestage such as polish instead of thowing away i just back it off to 1000 grit or 1000 to 500grit and so on . always ging to coarser stage and never back to a finer stage .
--paul