I've never tried feeding pollen substitute in the fall, but never had any luck doing any time that I did try except REALLY early spring before the maples bloom.
In 31 years I've never used Fumidil, but often one hive will take syrup when the other doesn't. I don't know why, but sometimes dribbling a bit down on the bees gets them more interested in it.
I haven't used Terramycin for 30 years, but it was commonly fed in syrup back when I tried it. I'm not sure why the powdered sugar would affect their interest in the syrup.