Note that there's now also the field Taxon sought but not found. The advantage of using this field over "Sought but not found" is that you don't need to give your observation an ID, and so it doesn't put a pin on the iNat map when people search on your taxon.

For example, if you enter a little blue penguin observation with "Sought but not found" set to "Yes", iNat still displays this observation on its map alongside all other little blue penguin observations. That can easily be misleading to other users.

If, instead, you add an observation with no ID and with "Taxon sought but not found" set to little blue penguin (Eudyptula minor), no extra blue penguin observation is added to the blue penguin map but you have still reliably recorded its absence.