I think it depends on the severity of the original coccidiosis; I did not retreat my girls after their 5 days and they were fine. Is your outdoor flock older? They are probably immune. But I really wouldn’t worry - just keep that Corid on hand and retreat everyone at the first sign of the parasite coming back. Like I said, even if you treat chickens that don’t have it, it won’t hurt them. I would go ahead and integrate everyone.