Sage I have caught a few triples but years and years ago in Michigan in a lake that had schools of yellow perch. if you didn't bring it in fast after the first one hit you would occasionally end up with 3.
The bad part of a multiple fly rig is when a bigger fish flops during the release and sticks the extra fly in a finger . i fish barb-less as i imagine most of you do but it still stings . If it was not for the bigger catfish i would give three flies a shot again in warm water. i do fish 3 flies for trout all the time although double trout are very rare