We recently received a shipment for one item out of a registry order that included two items. Apparently the other item is currently on backorder and won't ship for another month. Do I send the thank you note now or do I wait until both items have arrived? I don't want to be rude and wait too long but I also don't want to confuse the gift giver into thinking that we already received both items. I'm leaning toward shooting her a quick text message to tell her that we received the first item and thank her for it and write a thank you note once the other item arrives.