This is kinda fun! Be warned, I'm frequently wrong on this topic - I always think it'll be Ben and it turns out to be Ish and vice versa. Many of them can be determined by seeing who reviewed the show in their previous runs. The rest are just blind (and probably wrong) guesses. So for what it's worth:
Sunset Boulevard - Ben
Sunday - Ben (he did it at Encores!)
Significant Other - Ish (he did off-bway)
Glass Menagerie - Ben
Come From Away - Ish
The Price - tough call, but tentatively guessing Ben
Sweat - Ish (he did off-bway)
Miss Saigon - Ben? not sure.
Amélie - Ish, unless Ben is invested enough in Pippa to claim it
Present Laughter - Ish
The Play That Goes Wrong - Ben
War Paint - Ben (he did it out of town)
Oslo - Ben (did it Off-Bway)
Groundhog Day - Ben (did it in London)
Indecent - Ish (did it Off-Bway)
The Little Foxes - Ben
Hello, Dolly - Ben
Charlie and the Chocolate Factory - Ish
Anastasia - Ish
Six Degrees Of Separation - Ben
Bandstand - Ish
A Doll's House, Part 2 - Ben
