Nothing wrong with old stuff, it is great; but if someone rehashes a few old songs it doesn't count as a dated collection.

When you date a collection it is either that date that the works were collected or the date that they were created.   

People have been reworking old songs for years. If someone had reworked a few songs or tunes in the eighties that wouldn't be called "An eighties collection" otherwise we would have thousands of dated rehashes.