Not full blown hatches, young Jim.
What's funny is, in jan. I've seen single duns here and there and they nearly all get eatin.
In fact, a brown trout told me she "loved them!" and "they taste like a cross between bananas, chicken, and honeydew".
Having eaten sulphurs I will respectfully disagree with the brown trout, they taste like a$$ and are bitter.
It is a testament to that river that even sporadic hatches occur year round, I was just curious whether they were were full blown hatches or as you described.