Can I put drylok over older drylok
Yes, drylok can be recoated easily. Depending how bad (or not-bad) the spots are, you might think about whether the super-thick "masonry waterproofer" or the "concrete floor paint" is more appropriate. If staining appears to indicate leaks, probably the thick stuff.

Ease of re-coat is one of several reasons the concrete floor paint is on my shop floor rather than some fancy epoxy product. 5-6X cost differential and not being slippery (without having to add some surface treatment) are two of the others that spring to mind. And, of course, not being gray concrete...