re: The blaster shot on the AT-AT walker.

I think the issue is, despite Luke's line being "That armor is too strong for blasters!", the visual effects are more in common with shielding than armor. This also fits with the scene where, once the AT-AT is downed, suddenly it's able to be shot to pieces by blaster fire.

It's also why the blaster shot looks like it is absorbed rather than making a scuff mark or ricocheting.

I don't think it's a mistake per se, but rather it's the sci-fi concepts being played fast and loose with, and just not thinking it matters that much whether they call it armor or shielding. There was no way to know at the time it would be held up to this kind of scrutiny.

Short of drastically altering the visuals and spoken lines from the original, I think Ady has done the next best thing, which is to leave that issue well alone.

EDIT: Just found this, which should satisfy anyone else worried about it not making sense!

http://www.telegraph.co.uk/technology/news/7487740/Star-Trek-style-force-field-armour-being-developed-by-military-scientists.html