Ignoring the Ilford part it for the moment it is still a strange one. Having been on the Ilford tour on two occasions my impression was that the 35mm and 120 versions of the Ilford films in terms of ingredients are exactly the same. I'd imagine that if they were different then the 35mm and 120 would behave differently and yet they don't. I imagine the same applies to Kodak films where we have 35mm and 120 versions and yet Fuji Neopan 400 is the exception to rule
However somehow the 120 Neopan was configured differently from the 35mm version and yet I presume the characteristics of the two films were identical in the same way that Acros 35mm and 120 are the same.
There are more questions than answers and while I'll look at the info on the chemical via a web search I have a terrible feeling that it won't answer the question of why two films were or had to be configured differently in Neopan's case when in other cases such as Acros, the Kodak range and Ilford range they are the same.