[William Cloud Hicklin]

I expect that at all times, at least after then breaking of Thangorodrim, a greater or lesser proportion of the Orc population were free agents. Their natural tendency, after all, is towards anarchy and entropy! Even after Sauron hung out the "Grand Re-Opening" sign on Barad-dur, there was a considerable lag time involved in whatever bribes, threats or cajolery were involved in 'recruiting' orc-tribes to the Red Eye, and it's unclear that those of, say, Moria were ever working for him. I expect there were any number of "Avari" Orcs in the remoter parts of Middle-earth even during the War of the Ring. When Sauron went down his surviving Orcs returned to their previous sort of existence.