I just post the date in the allowed text when posting the SoTD:
It's not a perfect fix as in your wardrobe page it'll still show its "last worn" date as the day you posted, but it's the best solution I can find.
I recently did this with M/Mink as I had worn it quite a bit before it was added to the directory. So, my SoTD posts (using the SoTD tool) would look like this
Posting an old wearing of this because it wasn't in the directory at that time"