there are some subtle differences between the standard 3 d's and the maundy ones that look alike in Edward VII's reign and before, angle's of the rim etc, a good book to buy is  silver pennies and linen towels by Brian Robinson, goes into great detail about issues and dies telling proofs from standard etc, gone up a bit in price now, i got it when it was first issued, great book though  isbn 9780907605355