There are very few errors in the OT. I don't see any reason why Obi-Wan would lie about the damned droids. The mistakes are in the prequels. The most annoying mistake being why the droids would be in those movies in the first place! Just completely out of place, even more so than Chewbacca, because at least he only has a minor cameo and since the two characters never come into contact in the OT, it doesn't really create a plot hole like with the droids. It's just irritating.

It's the inherent trap of prequels to get them to match up with the existing story. And in a lot of ways, George failed, giving into the temptation of more flash and contrived connections that only allow for classic characters to make cameo appearances (and if George was really convinced we should watch them I-VI, those cameos wouldn't "need" to be there because we'd have no idea who those people are), rather than building connections that tie the stories together.

It's funny how, before 1999, no one complained about all these so-called errors in the original trilogy. That's because they didn't and still don't exist. Just because the prequels screwed everything up, it does't meant that the original trilogy has to suffer for it.