When making comparisons it's often necessary to alter the actual concentration to compare two developers it's the ratio's of p-Aminophenol to Sulphite that are important. The early BJP Almanacs had no final volume for their p-Aminophenol developer, it's still not listed in the the 1920's.
A problem is that 300gms of Metabisulphite, a litre of boiling hot Water, 100gms of p-Aminophenol then Hydroxide solution will have a final volume well in excess of 1 litre. Water is releaseded as well when the Hydroxidee reacts with Metabisulphite to form Sulphite. That's why I said "No final volume of solution is given but it's likely to be 2 litres if you want the equivalent of early Rodinal."
It's convention with formulae to make up to a litre with water, so while the BJP doesn't say that specifically for other formulae they publish the same formulae published by a company like Ilford or Kodak etc would. Ilford (pre WWII) said Water up to 1 litre, Kodak Water to make 1 litre.