Fermenting stalled

So I made a mistake.
I had 40 gallons (8 - 5 gallons buckets) of cider fermenting in the garage.
It was too cold and the yeast didnt do anything.
Airlocks were quiet.
Its been three weeks and I finally had room to move all the primaries into the house.

So can I assume I can just add additional yeast and will be good to go?

Probably shouldn't be an issue - and probably wouldn't even have to add more yeast, though might be a good idea just in case.

You might want to check nothing else has taken hold in the meantime - check OG to ensure it really hasn't moved (and taste, smell).

Once it warms up it might start on its own.

What was the temp of the garage? I've found with any fermentation wine, cider, beer you always want to ferment on the lowest end of the temperature range for your yeast. I use champagne yeast and ferment at 61F. Primary takes a few days longer but it ferments a lot cleaner and smoother. If your garage temp was below 45ishF you probably did stall it with temp but a lot of other things can cause it to stall too. Preservatives in the juice, old yeast etc. If you suspect any contamination, or if you are using a weak strain (beer yeast) definitely re pitch your yeast but stick with what you pitched already.

Thanks Barley-and-Hops!
The garage didnt get down that low (it was more in the 50's) and as luck would have it it DID ferment to 0!
I tasted each batch last night....definite alcohol!!
I will rack tomorrow.

I have read that cold fermenting can be a good thing and honestly at this point I think I like it vs the 60-70 degree range. I do believe from my tasting last night it did ferment smoother.

The only batch that didnt ferment was my hard lemonade.
So I repitched it last night and it now has airlock activity.

I think I will need to find a way to cold ferment in the summer!