You only get that message if you have said item in your inventory.

It would be better if it shows the account search result. Like "2 items found in your account!" You could then just click on the magnifying glass and check where those items are.

I just think it's unnecessary to only have it check your inventory, it's much more useful to know whether you stored those items in your vault/shop/gallery.

I've always thought this would be useful

Isn't this sort of like the "you have this item" on wishlists to a smaller scale?