That's not an easy one, unrecorded varities exist for many hammered coins all of which vary greatly in price from each other. Some types fetch little extra (or no extra) premium than a normal variant. In other cases they can fetch considerably more. The problem here is demand, how much demand would there be for the coin? Well Æthelred II pennies are not uncommon so there's loads to choose from and loads of unrecorded examples. Now to an Æthelred II specialist it may be of some value. I can't say at all with regards to this, but i'd probably contact Spink and ask for their opinion on the coin.