I am not advocating this, but my recent experience is interesting. I found some old pear (Gin) scion wood in the back of the fridge. It had been cut in early May, transported around the country, (not consistently refrigerated), and not treated particularly kindly. It was simply wrapped in plastic, with a dab of moist paper towel at the base, and then forgotten. When I came across it in the back of the fridge on September 15, it still looked in reasonable shape, so, as an experiment, I grafted a couple of pieces onto a pear tree in my orchard. Examining them today, (October 13), both appear to have taken, and one of them has actually foolishly started to leaf out. (The other has remained dormant, but has green, healthy bark and has obviously united successfully.) I am in zone 5b, and we have had a reasonably warm fall. ( We did have a couple of light frosts about 10 days ago, and the maples are all a blaze of red at present ) There is no particular reason why they should not survive the winter, and my conclusion is that the gospel specifying a narrow window of time in the spring when scion grafting can be done may be less authoritative than generally suggested. This also adds to my experience, (which I have noted elsewhere), grafting with scion wood which is well out of dormancy, (in one instance, with small leaves), although here I took a bit more care, and wrapped the entire scion with Parafilm to stop it from drying out prematurely.)
Broomholm OrchardZone 5b in Nova Scotia