There are at least three fixes that went in for Y2K issues after 4.3.3. Two of them existed in 5.0
If one of those is the change to the "date" command to treat a 2-digit year of 68 or less as being in the 21st century, I'd call that an *enhancement* rather than a *fix*, given that "date" accepted 4-digit years as of 4.1 - you can set the date to post-1999 years in 4.1 and later.
Do you happen to remember what the other change was?