Thanks again Mack - just read some posts about the Plaques on the Great War Forum - very complicated!
Here's a post, by 303Man, from 16 Feb 2016:
"These are all Acton Plaque reference Numbers:
3045 KIA OCT 14
70292 KIA 1915
75769 KIA 1917
88028 KIA 1916
142154 KIA 1918
151362 KIA 1916
162756 DIED 1919
171952 DIED 1917
176668 DIED 1916
177040 DIED 1916
178958 DIED 1917
181060 DIED 1917
189261 DIED 1917
214845 KIA 1918
224744 KIA 1916
302688 KIA 1915
As you can see they do not follow numerically by date of death, There must have been a system for the allocation and production of these numbers, I have the regulations regarding issue of the plaques and it mentions allocation of Reference numbers to sheets. I believe the sheets were prepared by Regimental record offices and then submitted, remember some soldiers were missing presumed killed and boards of enquiry were held to establish this, the passage of time would have created overlap and an early casualty's plaque being submitted later on with later casualties."
It also appears the number "29" behind the left ankle refers to the mould used in casting the plaque.
Very hard to see how we can, with any certainty, narrow down Pamela's plaque to John Keegan from Wigan - although the circumstantial evidence seems to point in his direction.