I've heard of that but never encountered it. One possibility;
This is one of the standard "random" groups, which use percentages to roll the dice for whether or not any ship will appear in that group. If the dice come up with the number for no ship every roll, this task force will have 1 BB, 1 CA, 1 CL, 1 tanker, and nothing else - no escorts at all. With 10 destroyers at 80% and 5 at 30%, law of averages you would expect to see about 10-12 destroyers total. Sometimes it will be 5, sometimes 7, rare occasions you'd see all 15 or none.
Somebody has some ambition they could go through all the mission files (preferably with some kind of text search utility) to see if there's a random group with some ridiculous number of destroyers in it.