There have been some cases when the data for a problem have been changed years after they first appeared. One instance is problem 8 (more digits), another is problem 59 (new text). I seem to remember there was more, but it's too vague to search for them.
In both cases the first entry in the discussion thread informs about the changes, but there is nothing in the problem description itself. In projecteuler.chat, "Clarifications on Project Euler Problems", there are posts by users confused by these changes. I don't wonder - it probably suffices for somebody to work longer on a problem to enter answers that were quite correct when he/she started, but are wrong now.
I can't see anything in the existing information in the discussion thread that would be too revealing in the problem text itself. So couldn't it be copied (and in future cases put there from the start)? Or what do I overlook?