Watson Webster and Wood release 1999/ 2000
I am not aware of a blank as scarcity appraisal.
They employ Purves rating system 3R = 4-6 copies known
Yours is Burrereo 2/10 usage 1904 to 1921
4-6 copies known? sounds doubtful, but what do I know?
I would certainly use Premier Postal's if you have the hammer correct.
WW&W only go up to "G"
Bobby or FDS may have a better reference there