Time uses the magazine "pull date" on its covers. Less important with fewer printed copies.
Interesting.
Doesn't make sense nowadays, when everyone gets their news in real time.
It's also confusing for future researchers. For example, if you want to read about 9-11, you wouldn't see anything about it in the September 15 issue of news magazines, four days after the event happened. You'd have to look for the Sept 22 or 29 issue, long after the news actually occurred.