Dave, I think a shelf life of 4-5 years is commonly quoted on this site, based on info at the Shell website. Your stash of M1 is safe.
I think the quarts of M1 0W-30 on the shelf at the local Walmart will probably sit & collect dust until November as many view 0W-30 as a winter oil in my area.
To view the many past threads on the subject, click on the search function at the top of the page & enter "shelf life".