I have them on the table for 3 sim days and they are not changing, I also think they are fresh in vase for sim eternity.
You can gift them in a box with a ribbon as anything else, and not shore about something else, but I do like the idea of using them as a decoration and selling them for fast profit.
I was also dissapointed not to find them in colllection journal but there is a pattern of 3 common, 2 uncommon, 2 rares and one special collectable or maybe 3 uncommon. That is why I said I think I got them all as I placed a lot of spawners and kept getting these. Cosmos as a special flower is not that rare at all actually.
Counting that if there is more, it will eventually be reported by those who find them