According to: https://mirror.codeforces.com/blog/entry/68204
MikeMirzayanov announced a way to uphack recent problems for Div.1 participants. I'm curious to listen to the details on why this is limited only to last week problems. He clarified why it was limited to Div.1 participants but not why only recent problems.
I mean, for instance I believe that Educational Round 3B is hackable with this test case (as many participants don't use long long for the length of the frog's tongue):
1 200000
1 0
1 1000000000
1 1000000000
1 1000000000
...
So what is the harm in enabling uphacking for old problems as well?
If I remember correctly this was asked before and the main issue was that if there are validator / checker bugs in older contests that cause unexpected verdicts with cases not seen in the contest its not exactly feasible to contact whoever wrote those contests to fix them.
Mike has answered your question in this comment
An uphacking can be applied only in case of a formal and complete validator and perfect solutions. For very old contests we can't guarantee it: problem writers and coordinators probably left Codeforces. Are 7 days really too short? I can extend it, but not for infinite: I like the idea of "freezing" a problem, it helps to move forward not spending much time on supporting old. For problems out of official Codeforces rounds we can't be sure about validators, so an uphacking can't be applied in general.