I am currently running a long, in-depth, story-focused campaign that has been going on for months and seems to be well-liked among my group. As you might imagine, creating a world that we play in for that long, I come up with lots of new ideas for characters, adventures, and even little things.
I spend a lot of time making sure everything in this incredibly intricate story is consistent, but, of course, I do make small errors from time to time and forget little details. One of my players has an incredible memory and often seems to remember me saying things months ago that I can't even remember. I have no reason to doubt he is lying to me.
That in-itself is fine (it's quite useful, actually), but the bigger problem is that things I add to the campaign cause problems.
Today, for example, I made (what I thought was just a little joke) that one of the NPC characters now speaks more languages than him. He said that's not possible because I (apparently) said some time ago that the his character spoke all the languages he could ever need. If I said such a thing, I suspect I didn't mean it quite so literally. Since that time I have indeed created one new ancient language for an upcoming adventure.
Now, I'm quite happy for his player to learn this one to, but the NPC who has it does so because it is an ancient language and they have 43 knowledge history and 25 linguistics: more than enough to understand it. His character has 0 history and 13 linguistics. He is personally offended by the whole incident.
The bigger problem: if I try and discuss the argument with him, he acts as if he didn't get upset at all which, in fairness, is difficult to prove because he tends to be more passive aggressive.
How can I go about making small changes like this one without it things crumbling? I know I am probably at fault here too.