I have found a site which in the past I have found to be reliable. it is called Ilford memorabilia and covers the history of MG paper and filters. If it is to be believed then the need for a calculator was before MGII filters.
The essential differences between MGII and MGIV filters appear to be two-fold:
1. The MGIV set is 12 filters and includes an 00 grade whereas the MGII is 11 filters with no 00 grade
2. Both work fine with current MGIV paper but the older MGII filters have the same exposure for grades 0 to 3.5 with twice the exposure for grades 4 and 5 whereas the MGIV filters have the same exposure for grades 0- 3 and twice the exposure for grades 3.5 to 5
In another search of APUG threads I found a reference to MGII filters by an APUGer who made no mention of his MGII filters "not working" with current MGIV paper
So it appears that unless Huub was referring to the set of filters before MGII filters, then MGII filters operate OK with MGIV paper with a slight variation on which grade onward requires the twice exposure routine.
All of this of course assumes that I read Huub's post correctly. He might not have been saying that MGII filters need a calculator and neither might Simon Galley. It was simply me that was misunderstanding their posts.