Icing can happen anytime of the year as I was reminded on a trip to Mull last year.
I've never picked up any significant ice in stratus but I got distinctly uneasy about the ice I picked up in MAY in solid IMC in the cumulus above the Scottish hills. I had an escape route out over the sea and descended from about 5000ft to 3000 and was then clear of cloud (as expected) but it was a good wake up call.