This short article illustrates a possible new variety of Edward III pennies of York; the original article was revised after D.I. Greenhalgh provided helpful input. Here is the amended version (Jan.17th).
Edward III Pennies of York with Saltire-in-Quatrefoil Reverse – Mike Cuddeford
BNS Research Blog 
Now being able to view the other images I am now certain that the central cross is a deliberate addition, and quite possibly be entered using the Saltire stop punch. I Agree with the author ( from email correspondence) that it is worth flagging up.