Hi,
Welcome to the Forum.
My initial thoughts were the same as Phil's, that the mark is not in the
Sheffield Assay Office Register, but B.W. Watson in his preface to the book states
"In some cases manufacturers have used the same design of mark for a long term of years and new entries have become necessary, from time to time, in consequence of the punches wearing out, or from other causes. Under circumstances such as these the original entry only has been given". So I presume that John Law did make a later entry without a pellet, or course it is always possible that on your example the punch became loaded with debris and the pellet not struck.
We have that mark attributed to John Law, see:
http://www.925-1000.com/dlSheffield2.html#MSimon Moore in his
Cutlery for the Table notes John Law as a maker of folding fruit knives.
Trev.