The current market values the Grant name at the second level of Brand Value, BV2 (3/4 the value of an "identical" gun with a BV1 brand, which is Boss, H&H, Purdey, and Woodward). As for quality, best work Original Quality, OQ1, can come with any name on it. No name in the gun trade had a lock on superior quality. Shops were run by masters and they all knew each other and who could do what work to best standards. An skill, level of skill, or supply of skill missing in a shop's in-workers was covered by contracting with out-workers.
The trick here is to firmly separate brand name value from original quality level. It is far easier to learn the values of brand values independent of quality. Then, learn the values of quality level independent of brand. Lastly, add the value of current condition level and, presto-alakazam, you have a value for the gun.
