I have a late blued Webley Junior air pistol that is coded B.
Unusually it has what appears to be a date code under the left stock side: 11 8 for November 1968. This being stamped in a similar manner to Webley Premiers of the same vintage.
If you do remove the grip to check yours, be very careful when replacing it to ensure the moulded projection at the grip's base does not sheer off (if it has not already done so).
Hope that helps.
John
Currently looking for Baikal Makarov pistols with the following prefixes to the serial number: 98, T01, T09, T21, T22
Prefer boxed or cased but will consider loose examples too.