I don’t have the print that I sun bleached, or maybe I misplaced it but I recall there was a density loss (by eye): maybe the different forms absorb different amounts of light. I would have to repeat that experiment. I do have my FAL soln still. It did not mould over 4 mos, and does not go blue when mixed with PF so seems pretty stable.
Regardless, it might be a useful cyanotype salt as it does bite better into the fibers making a denser less mottled print than traditional FAC, but I have not had a chance to explore it more. Maybe someone else such as yourself will be able to confirm.
Here is a colour comparative of the different sensitizers( w/v)
FACG ( ferric ammonium citrate- green 25%)
FAL ( ferric ammonium lactate 35%)
FAO(ferric ammonium oxalate 25%)