Hi,
I'd always expect to see a few - it depends on how much they struggle and how you hold their neck as well.
I don't routinely check though - I'd only stress them out like that if I had seen behavioural clues etc that made me suspct an R.I.
When you are in there at that point I also look for yellow cheesy spots, red and inflamed areas ( though I have seen some that bit their own mouths while struggling ), and signs of swelling or irritation around the end of the trachea as well as the amount/ consistency of mucus.
Also look to see if most of the mouth is a nice healthy colour or if it is too pale.
dr del