what I have heard is:
it's not polite to do it in one event:
Originally, a kata is a precious gift, so you offer it to the lama, the lama gives you another.
but nowadays lama just put the one back to represent that he gives you one too.
OK, we all reuse katas, which I think it's fine, but if:
there are more then two lamas there, you give kata to one first, he gives it back to you, and you give the same one to another lama in front of all of them.... it would be a bit strange.
The polite way is: you should prepare katas for separate lamas, so in the end they will all be on your neck at least at that time. After they or you leave the place, you can collect katas for next time use.
Tibetan people or monks might feel it's funny if you use one kata to give to different lamas again and again.
But to be honest, there are too many things we non-tibetan do would make Tibetan laugh. Maybe it's not a big deal.