Your air samples could change, and if you exceed the PEL when an OSHA inspector is around and your men aren't wearing respirators, you're sunk. Pacific Solutions reached the same conclusion. Percussion power tools can jar loose and peeling paint off the substrate outside the shroud. The vacuum system may malfunction and a worker with earplugs may not hear signs of trouble. To err is human, and painters are human.
Contractors take the cautious approach recommended by consultants.
I'd rather go overboard on safety than risk hurting someone or losing my business. On the other hand, a half-mask respirator is less expensive than the more elaborate face gear you must wear during abrasive blasting. Similarly, paint removal with low-dust power tools generally demands less containment than abrasive blasting. Because lead emissions can be stifled, contractors are getting by with a tarp on the ground to collect stray paint chips. That's a far cry from the sealed and ventilated booths erected along bridges and water tanks for abrasive blasting projects.