Yes, very definitely. Assumed band is applied to propertes if the VOA haven't had chance to band it yet. Anything you pay obvously goes to the balance of the charge and any overpayment can be refunded to you.
If it s assumed bandng, you can contact the council and have it changed if you like but, say for example you ask for it to be given an assumed band B and then VOA come along and say it's band C and they do this in January, you only have untl 31st March maximum to make up the shortfall.
If it's confirmed banding, give VOA a ring and get an appeal in if you don't agree with it but you best be quick. If I remember correctly, you only get 6 months from its banding date to appeal.
I work in the c/tax dept. for Stockport council two and a bit days per week.
Ps. It will say "Assumed" very clearly on the bill if it is. If it doesn't, it's been fixed banded. VOA will sort you out, they're pretty efficient.