VS will take returns for up to 90 days with a receipt.
From their website (this is for web purchases, could not find a store return policy)
We take great pride in our reputation for quality and excellent value. If for any reason you are dissatisfied with a purchase, we'll assist you with a prompt refund or exchange. No sale is final.
Refunds for items returned within ninety days of the purchase date will be credited in the same form as the original payment type.
Refunds for items returned more than ninety days after the purchase date will be in the form of a merchandise credit redeemable with your next purchase.
I assume they would take back a bra (with no obvious signs of wear) if THE TAGS WERE RETURNED WITH THE BRA. They wouldn't take it back without tags at all. As for the thongs, I don't know of ANY store that will accept underwear (unless packaged in plastic and unopened) to be returned. I know in PA, they state that they cannot accept underwear returns BY LAW. Any store that takes a return based on the receipt will mark the receipt items as returned, to prevent stolen items from being exchanged for cash with a legitimate receipt.
As for the sizing - my husband couldn't buy me a bra if you paid him to, so I don't know about that. Depending on the bra, a mistake could be made. Some of my bras look a LOT bigger than others.
But, based on your other questions... I think you already know all these answers.