If a plan previously had a benefit formula with under the old integration rules (before 1989) and then continued to provide for disparity under the newer permitted disparity rules, does the 35 year cap on YOS include both years earned under old integration rules plus years earned under the newer permitted disparity rules (vs. just starting from 1989 forward) ?? I'm thinking it includes both but would appreciate a confirmation if true.

What 35 year cap? I think you can integrate on 100 years if you satisfy the cumulative disparity limits, i.e. reduce the excess percentage.

Yep. I have seen a formula which used 0.5% times service (max. 40 years), which is less than the 22.75% overall maximum.