Oh, that sucks. That has happened to me a few times. January thaw sends the birds into a molt, then it freezes back up again. It's often the hens who miss their Fall molt. Never a fun thing to deal with...In the 10 years I've had chickens I've seen all sorts of molting patterns and times. Some seem to do more of a "lose one, grow one" thing and never look bad, others look like they narrowly escaped the feather plucker. Most are in between.
Some start early, some late, most in the middle. I had one that didn't have her first moult until she was 1.5 years old .... at the end of January, the coldest time of year here in Vermont. She didn't seem to suffer for it but after that she "decided" that fall was a better time.