After moving a site, new posts show, old ones don’t, but all ARE in the database

Hello. Some time ago, a colleague I’m assisting moved his website to a new hosting company. The problem is that only the new posts he’s made show up–not the old ones. Yet, they are all in the very same MySQL database. I am trying to help him out because I thought he was having the same problem I had when I moved my databases (which was a simple fix) but that isn’t the case.

Can anyone advise on what may be causing this to happen, and how to make the older posts show up? Thanks.