3 things you want to avoid when storing grains are heat moisture, and exposure to air. The bins are tightly fitting but is there a lot of air space in them? How hot did your garage get?
I left some specialty grains in my freezer for about 3 years. The ones that were sealed with most of the air removed were good and made good beer. I had one zip lock bag that wasn't tightly sealed and the grains were kinda soft and didn't taste fresh. I threw those in the trash.
I would say taste your grains and if they are crunchy and taste good go ahead and try a batch. If you do use them let us know how the beer turned out.
If you don't want to risk it, just replace the grain with fresh.