I echo Kristy's comments. I have never seen an initial pre approval good for more than 90 days. However, I have seen some for less (30 days, 45 days, and 60 days). That being said, if no major purchases have occurred and no changes in income have occurred in the pre approval period, most lenders can extend them.
That being said, if you are 12 months out, then the pre approval will only give you an indication of your status and what can get approved for now. Much can happen in a year to change that for the better or worse. Good luck.