We have to remember that Agfa's parent company was already a highly sophisticated chemical manufacturer by 1897 so it's likely that they had a high degree of control over the purity of chemicals like hydroxides used in developers.
Originally Posted by Kirk Keyes
Reading work by contemporaries of Andresen working with similar developing agents they were aware of the differences between the free base & different salts of compounds like p-Aminophenol.
Mees & Sheppard did work with p-Aminophenol back in their days at Wratten & Wainwright, how much I don't know without trying to find copies of the book and papers they wrote (while at Wratten). This work is held somewhere along with the work of J.Desaume in Kodak archives.
Kodak also researched p-Aminophenol, Sheppard's name crops up again and their choice of salt was p-Aminophenol Oxalate (Kodelon) which presumably what they used in Kodinol.
George Brown, the Editor of the BJP from 1904 until 1934 would also have been well aware of the differences between the free base & the hydrochloride, (he was himself a Chemistry Scholar) he would have known Mees & Sheppard, he lists their Wratten Formulae in the 1910 BJP Almanac and makes a point of listing a concentrated p-Aminophenol developer, alongside a p-Aminophenol Hydrochloride developer.
What's perhaps more important is we know that by the 40's and through to today Agfa/A&O and Calbe have definitely used the free base, so any attempt at making our own needs to do the same.