I think Puriclean was out long before Milton - we used Puriclean in the mid-80s for our first caravan.Although I seem to recall that on earlier caravans sterilising fluids like Milton were ok’d in the Owners Manual. Or is my memory fading? When Puricleans came along I changed to using it.
In 2010 the CC (CMHC) were advising go by Truma/Carver recommendations with one of the advised fluids as Milton2. Now the CMHC are far more general with no chemicals mentioned. it is not 'outsmarting " the makers but a recognition that things change over time and not everyone moves at the same speed.