Would a 13, 16 and 20 qualify to be a Downbeat or must it be 12, 14 and 20?

The ONLY configurations that qualifies as a Downbeat are 12/14/20 and either a Downbeat snare drum (4 X 14) OR a Supra. That's it. Anything else....ANYTHING else is NOT a Downbeat.

okay, with that rule in place...what would a 1969 13, 16, 20 kit be?

There isn't a name for that particular configuration....although at this point in time there SHOULD be one, because I can't tell you how many of this configuration I have seen! -LOTS!

But, the "rule" is set by the company's catalog depictions for the most part -there are exceptional circumstances that had to do with printing dates and the re-use of old catalog photographs and descriptions from previous years, etc. In general, though, Ludwig named their kits with names -Super Classic....Hollywood....Downbeat....Jazzette....and so on. In all those years, there was never a 13/16/20 configuration that was "named"

The only real significance this has is to collectors who prefer to try and get things in as close to original condition as possible. Functionally, the drums are great sounding drums in ANY configuration. Unfortunately, they usually don't bring as much money when they come up for sale lacking an "official" moniker.

thanks O-Lugs!