Bear in mind much of WDADU was written before Charlie joined Majesty/DT. In fact, I believe the only things on the album that were written with Charlie were Status Seeker, Light Fuse And Get Away (maybe), the lyrics/vocal melodies for Afterlife (the original version of the song with Chris Collins had completely different vocal parts), the Spanish guitar intro to the Killing Hand, and a few little other odds and ends (I recall Charlie saying somewhere, I think it was in the book for the 2004 remaster of the album, that the military snare part in TKH was his suggestion as well). The point being that most of the album was still written for a singer of the Geoff Tate or Bruce Dickinson type. In fact, it's rather ironic that To Live Forever, which was very much written with Charlie's voice in mind, was never properly recorded with him singing, just a rough demo from '88, while the versions of the song that were recorded with James in '91 and '94 were all very professional and of album-worthy quality.
Instrumentally, yes just about everything was written before Charlie joined the band, aside from Status Seeker and perhaps Light Fuse and Get Away. However, I don't believe any of the songs had all the vocal melodies written before Charlie joined the band. Keep in mind how Charlie got the gig in the first place - when he first met the guys, he tried singing their older songs (from the Majesty demos) and he couldn't cut it. But then he asked to try singing one of their new songs that apparently didn't have vocal melodies written yet, and it was what he did vocally with that new song that got their attention. Another example that proves this point (and is evident on the WDaDU Demos official bootleg) are the vocal melodies for TOWHtStS, which I believe were re-written several times before they finally came up with what is on the album. And as you pointed out, Afterlife received all new lyrics and vocal melodies. So I don't really think much (if any) of WDaDU had the vocal melodies pre-written before Charlie came into the picture.
See, I've always gotten the impression that whoever wrote the lyrics to a given song also mostly wrote the vocal melodies to that song as well, so since SS and Afterlife are the only songs on the album that Charlie has writing credits on, I assumed that those two songs, and maybe LFAGA, are the ones where the vox parts were primarily written by, or at least with, Charlie, and the other songs were considered more or less complete when he joined the band. Now as you pointed out, he got the gig by showing how good he sounded when he sang in a manner that was more comfortable for his voice, so they mostly likely let him put his own spin on all the songs regardless. All that being said, though, it's still pretty obvious that, vocal melodies or no, most of the
music on that album was written for a more metal singer (Status Seeker being the notable exception).
For what it's worth, I think Charlie's voice fits most of the album well enough, but it really emphasizes the band's more 70's influences, especially Rush and Kansas, and down plays the more metal sections of the record that were intended to sound more in the vein of Queensryche or Metallica. That's why Charlie sounds better on lighter, poppier songs like Status Seeker and To Live Forever; his voice is just more well suited for that kind of music.
Also, on the main topic of the thread, I have most of the YtseJam bootlegs, but the only ones I listen to on a regular basis are the FII demos, as I prefer that version of the album to the final product (aside from BMS/HK). I also listen to the NY '93 boot fairly frequently as well, as it's great to have a decent quality recording of a complete I&W -era show, plus it has a better version of the old ACOS then what is on the I&W demos. But beyond that, the others are mostly just curiosities for me; cool to have, but not the sort of thing I break out on a regular basis.