You get a +1 from me for a good ending with the Level 4 addition, though I do agree with TL333s assessment that it's basically 507 but time instead. One sentence confused me even though I got the gist:
"An updated copy of SCP-2896’s containment documentation should be maintained in a secure storage locker along with all previous containment documents have been found in (see addendum for more details)."
Something about the sentence structure is weird. Maybe just take out the "have been found in"?
ETA: Another comment after mulling over the Level 4 bit: would the separate iterations of the Foundation attempt to establish a model of 2896's timeline somehow? Like at least for the current Foundation, I would think they'd try to carbon date or measure his telomeres to gain perspective on when he is in regards to himself.