Yep, buy what you love, leave what you're on the fence about. If it's something that is carried year round, it will most likely not go on sale at other times...If it's a popular item it may run out and not come back, though, so you never know!
With store brands, they have to forecast really far in advance, so if they run out they may not have it again in time to be on sale. If it's a basic item, it may come back and full price and then go on sale during the season, but if it's a nonbasic it will likely just be gone. If it's a nonbasic that isn't popular, though, it will probably go down to 60% off in the middle sizes.
With non store brands, they can pull inventory from the company where they are selling to more than just Nordies, so they can sometimes bring in more of a popular item once they see that it's selling down. the leftover merch will likely go on sale again in time to compete for labor day sales, though.
So, it's all about gauging how popular the item is, and if you think it will be left in stock at the end of the sale, as well as kind of knowing the supply chain processes and how likely it is to be stocked longer term or not.