At large gateways and foreign cities, there are usually First, Business, and Economy lines for international check in. Which line can Premiers use?

The reason I ask is because I was flying international out of ORD back in May and it was very unclear, so I just stuck with the Economy line.

I got bumped and was flying in Business Class the next day, so of course I used the Business line. There was a "concierge" policing the line, confirming that everyone was traveling business class. The same concierge told a 1K that the first class line was for first class tickets only, and 1Ks could not use it. (The Business line actually was very long.)

I also flew on Lufthansa recently, in Economy, and used the Business Class line, even though it says "Star Alliance Gold" and Premier is "Star Alliance Silver". I was not hassled, but was I actually eligible to use that line?

Then I see other variations... in EZE, UA has a special line for Premiers, which is a real treat because the regular Economy line is a complete zoo.