"Our intelligence officials estimate that Saddam Hussein had the materials to produce as much as 500 tons of sarin, mustard and VX nerve agent.

State of the Union Address
January 28, 2003"

To me that isn't a strong statement. And it's accurate.
And I know I heard the entire speech
As for your other references. First, it's hard to know the context- no links are provided and failure to do this isn't a good sign.

Look at early quote:
"We know that the regime has produced thousands of tons of chemical agents, including mustard gas, sarin nerve gas, VX nerve gas."
Cincinnati, Ohio Speech
October 7, 2002 "

Bush in Jan 03 said "had the materials to produce as much as 500 tons", whereas early he said "thousands of tons of chemical agents". So in the big speech which million are Americans are going to listen to, and a speech which gone over very throughly, Bush has used a limited estimate.
Now, I suppose you want to call this lying.
But Saddam has had during his regime chemical weapons, because he said he has used them, we have documents shows these weapons used to kill citizens and used them to repel Iranian mass assaults in Iraq/Iran war, etc. So to say Saddam *had* "thousands of tons of chemical agents" is reasonable. Whereas it's less likely that Saddam actually used "thousands of tons of chemical agents" on people or that Saddam at *one point in time* had "thousands of tons of chemical agents".
Now, the Jan 03 speech doesn't say Saddam has this material or has up to 500 tons of chemical agents. Rather the speech said "had the materials to produce as much as 500 tons". Bush is accurately referring to the then current UN inspector report.
In other words Bush did not lie nor even exaggerate, but instead used what was consider reliable intel data, to inform the public of potential threat to national security. Now, Bush is a politican. You can't expect that a politican would describe the world the way a scientist would. We don't generally elect scientists- and there is a good reason for this. Scientists manner of discussing issues is not the manner in which will leads people anywhere. Now, there is no reason a scientist couldn't become a politican, but he/she would need to change the "style" of discussing a subject.