Here is Jessi's post from a while back regarding BNS vs BNR treasuries:
Many are asking what a BNR or a BNS is..
BNR: Buy and Replace. If you purchase something from a shop featured in a bnr an item from your shop will replace the item from the original featured shop. If someone then purchases an item from your shop their item will replace yours..
BNS: Buy and Stay. If you purchase an item from a featured shop in a bns you will get a spot in the following round, and you will stay featured until the next round. There are bins sales in rounds 50 and 60 etc, so if u keep making purchases you keep moving on.