Serial Number Axxxxx

im somewhat confused by your question , not certain which rifle series we might be discussing , but ill have a go at this as a no4 mkI as they are common these days ,

an"A" prefix with 5 digits , would have been assigned to maltby if first "X" is a '1' , FAZ if its a '2' , BSA if its a '3' or

BSA was assigned  '4' thru '7' in the prefix "A" only

makes it a FAZAKERLY rifle , a mkI originally , but it might have been converted to mk2 by either FAZ or BSA to a mkI/2 , but if that happened it should say so ,

FAZ marks their rifles left side of the reciever , should say ....... no4 mkI ROF[F] , but ......

if its not a no4 rifle we start back from scratch , these are generally marked on the right wrist ,
a little less data on the numbers but the "A" prefix was used by

-RSAF Enfield in 1907 , 1912 , 1913 , 1915 , 1917 , 1918 , and 1920s
-BSA in 1916 ,
-RFI in 1916 , 1965 ,
-Lithgow 1918 , 1920 , 1921 , 1922 ,

most of the PF series were 'contract' rifles , they were all mk2's , referencing these leads me back to the no4's and my previous info