In general, its his agent that manages his IMDB page, but corrections and additions can be made by anyone with first hand information. I have been allowed to make additions and corrections as I have been vetted as a reliable source. Its been some time since I have done so, as I do it only when I receive creditable information from authorized sources. Just because someone sends me an email doesn't mean the info gets added to IMDB, but if it is from a trusted or official source I have done so as to expedite the information being added. He's definitely off of Gunned Down, which is a relief, really as it still appears to be a Z-grade blood and bullets junk film. He's still on board Maudie, but it has been pushed way back into the second half of 2015 and is still scrambling for funding. Caesar has also been bumped to second half 2015, but Sean is no longer on board and they have yet to recast the part. Depending on scheduling with Martian, which has just started filming, he may or may not be able to pick that back up. Caesar is also not yet fully funded.
I'm not surprised at all the jumbling about as it is rather unusual for him to have more than 3 major projects going off in the same year. I'm sure the most lucrative for him is The Martian, and perhaps his role is more involved than what he usually gets in these sorts of projects. Regardless, whoever did the editing on his page did a real hatchet job by simply dropping projects completely before any any official word has come out about them. I say "official" announcements because those 3 missing projects were heavily announced in the first place. Personally, I'm quite please to see Gunned Down gone. That one had disaster written all over it.