Are there any exceptions allowed? I'm pretty sure I've had a major nationwide pharmacy give me a bottle with pills from two manufacturers in it. It had pills from the first in the bottom of the bottle, then a cotton wad on top of those, and the pills from the second manufacture on top of the cotton ball.
They opened the bottle when I went to pick it up, and pointed out what was going on inside and made sure I understood. They explained that they did not have enough pills in stock from the manufacturer they had used before for that prescription and refills, so filled out the order from a different manufacturer.
Perhaps it does not count as commingling because they divided the bottle into separate champers with a wad of cotton?