Cabby and Swallowtail bulb holder covers

I've never heard of these before or seen them for sale but assume they are a standard part

They clip on to the bulb holder on the back of rear lamps inside the boot if that makes sense

I've just stumbled across 3 of them in my loft, just wondered if there was any rarity or value to them

I have about 6 of them myself.... I think I just picked them up at the yard.....they were free....