User blog comment:FloaterJ/Nitpicker's Nook/@comment-25176701-20150217033452/@comment-25869525-20150219003003

I haven't paid enough attention to that detail, but yeah. Figure there were 100 of them originally, plus Bellamy. Subtract a dozen or so that died along with the 47 still under Mt Weather. There should be only 40 or so of the delinquents milling about. Once an extra is hired for one of them, bringing them back for later episodes gives us consistency, as in "Oh yeah. That's the guy from the episode two weeks ago."

Besides, it makes sense from a production standpoint too. Wardrobe already has clothes that fit them from the first time they used the person.