Another example, serial number 366, has been brought to my attention by a respected member on here, who is fortunate enough to own it. So that brings the number of known examples up from seven to eight, with the following seven having confirmed serial numbers:

124, 234, 274, 298, 344, 366 and 397

This makes no difference to the rarity and desirability of the gun of course, and so (IMO)it should easily make £1500 at auction.