It's not that the "new" articles are recycled old articles. It's that the older articles are being reintroduced and featured on the front page for people to see. T-Nation's published 3,200+ articles over the last 17 1/2 years. Not only have some people not read them all, but there's still plenty of solid info that can be dusted off.
The dates are included with the posts to give a frame of reference, but they're being reposted so that someone who just discovered the site (or even someone who's been on it for a decade) has the chance to read a Poliquin article from 2000, for example, and find a nugget of gold that suits their own training.
I'm not totally sure what the reason is for jumping around to different articles through the years, but I do think it'd be even more strange if they just started over from the very beginning in May '98 and just reposted things day by day 100% chronologically.