According to :
Is this done? Are their hidden problems waiting to bite me if I install
new 5/4 x 6 boards on top of and perpendicular to old ones?

You'll have greatly accelerated moisture/rot/mildew problems,
because you're essentially routing water into a "trap" that'll
take a long time to dry out.

Don't do that. Tear off the old layer.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.