Look at the projects section @ "Frank Wildhorn" and "Someone Like Frank". He is working on (sue me if I left any out...) "Camille Claudel", "Waiting For The Moon", "Alice", "Bonnie & Clyde", "Excalibur", "Mitsuko", "Cyrano De Bergerac", "Carmen" and "The Count Of Monte Cristo". Who here has seen "Camille", "Waiting...", "Never Say Goodbye" and "Rudolf"? Do any musical themes recur? Does Frank recycle music from show-to-show? It'd be too demanding and too crazy for one person to write 20/30 songs PER SHOW like this. I can't fathom it.
Well, I know he has numerous songs that are, in his own words, "awaiting a musical." For example, "Anything Can Happen" is a relatively old song that Frank wrote and is being used in "Alice." While it's possible that was the original intent, I doubt it. Also, "Only Love" appears in Rudolf after being cut from Scarlet Pimpernel.
Other tidbits: The original draft of Jekyll & Hyde's use of "Ballad of Jekyll & Hyde" was a blatant rip offs of Sweeney Todd. Also, I've read that a few bits were eventually used for Pimpernel. Since then, Wildhorn definitely does seem to have his own style with his musicals though.
"If I Should Lose My Way" was an original song that was ultimately incorporated into the For The Glory score.
Considering the majority of most of his music is "pop" music, similar chord progressions are bound to occur as well. The gothic "theme" is also an obvious recurrence.
From my memory, "Anything Can Happen" was always connected to "Alice". I listened to the song, on Linda's album, and it didn't seem to have any connection to the story. As a matter of fact, the style of the composing & the lyrics reminded me of the beautiful 1985 tele-musical with Natalie Gregory as Alice. It has a host of stars, and it's one of the only versions with most of "Through The Looking Glass" incorporated. I still remember being excited when I heard that Frank was going to develop the project with David Copperfield. But nothing's been said about that since.
"Only Love" was written for "Rudolf" first. It was then interpolated into "The Scarlet Pimpernel" where it was later dropped. It found its home again in "Rudolf" where I think it would work better. I've never seen "Rudolf" but the song always sounded jarring in "Pimpernel". Probably for this reason.
You're also right in that there's only so many chord progressions you can use. But how does Frank do it? It amazes me how he sits there constantly being able to write tunes. Not to mention Jack whos whipping up lyrics for about a hundred projects.