this is actually a great question and think it deserves some more discussion and learning, such as what Fichy just gave me..
I say the window opens back up pre spawn, sometimes as early as late Feb if the sun is high and ticks that temp in some areas back up a few degs on the water in the afternoon.. I have had success with the streamer (SRS) if the winter starts to break up early and the steelhead start to spawn early.. I also think you (fichy) seen some chrome chasing baitfish in a warm feb day after a mild winter..
While I didn't , don't strip my fly, rather just swung it, I don't see why stripping wouldn't be effective..
Another reason for my march-april timing is largely due to the amount of salmon fry in the river.. When Fran V says it's his #1 spring pattern from back in the late 80's-90's while he was guiding, well guess what, I listened and bought his book about the Salmon River and patterns..
I believe he also held (holds) the world record coho on 2# tippet, at least it was back then ..
Finally a third element into this is that my Dad, the great one, didn't like using bait.. He liked casting spinners, spoons and lures for steelhead, he caught plenty from mid march-april while I struggled with egg sacs & flies (on spinning rod) .. Of course some of his favorites were panther Martin single hook with beads on the lure shank before the hook, his spoons were blue fox pixie and little cleo, lures were of course rapala in rainbow trout..
Now granted, you fly guys can whip loops around me /cast and swing patterns FAR better then this old spinner so some things I may say are irrelevant to the knowledge you all possess.. The words you type and speak are ALL influential to me..