Are you talking about the nasality becoming prominent? In my opinion, the first (albeit very subtle) signs of Jon "singing through his nose" appeared on the These Days album. For example, the lower parts of Hearts Breaking Even sound a bit nasal already.

In my opinion, his voice was pretty much the same throughout 1995-2011. It became more nasal after '06 (while on the other hand his range grew drastically during the second half of the LH tour), but you could still tell it was the same guy singing here...

https://youtu.be/WGJwBPgqxWA

...and here:

https://youtu.be/ZjiHpv0MVlk

Jon did sound different in 2010 than he did in 1995, but the difference wasn't HUGE.

PS. I think his dropout on the BWC tour was largely due to technique-based vocal exhaustion, which (in a very similar way to the Slippery run back in '87) basically killed all of what was left of his voice at that time. The inconsistency he's displaying nowadays was certainly apparent back then already - as this video proves:

https://youtu.be/OtQeL3c3dsM

Jon goes for Always like it was the last song he'd ever perform on stage, nailing most of it, and then can't sing These Days to save his life. Singing all those high-pitched songs with an unhealthy technique does take its toll by time. (Of course the stress must have been a factor as well, but I don't think that after all these years to recover, he would still sound as bad as he does now if his cords weren't f***ed up.)