I've been playing LeafGreen recently and noted that when you battle Giovanni in the Viridian Gym, he has a Lv50 Rhyhorn, not a Lv50 Rhydon. He still has that Lv45 Rhyhorn too (i.e. he has two Rhyhorn). This needs to be corrected in:
http://www.psypokes.com/frlg/gymelites.php
http://www.psypokes.com/frlg/walkthrough.php?part=16

Although I want to say that you might want to wait for Jigglypuff or another mod to see this, I must agree with you that the pages must be changed. I recently just went through the whole LeafGreen, up until the Elite Four battles, without saving, as I had an awesome team in the save file and I didn't want to delete it. I noticed that Psypoke said that there was a Rhydon in there, but there isn't. Giovanni has two Rhyhorns.

While we're at it, I remember training up my Pokemon to fight against Koga's Weezing thinking it was at Lv43, but it was only at Lv37.

I'm guessing they had R/B/Y in mind when they did the walkthroughs and gym leader stuff. Well, the first time I ever had LG, I had a lv. 51 Venasaur and lv. 50 Fearow cream Koga. I didn't know that Psypoke existed at the time, but still, I thought Koga would be tough. He's so easy now! (Even if I started a new game, that is)

TM44 Rest is found on the SS Anne, not Route 9 according to the TM/HM list in FR/LG. I double checked this by playing through Route 9 in LG.