Those are it, as far as I know. What happens is that very low PQ planets get more than one tile of each type (up to 6 each yellow/orange/red for PQ1s in DA, IIRC up to 3 of each on a PQ4 in TA). That means a PQ1 often ended at PQ19.

The weathr zenith and biosphere modulators are TA-only. Using both as well as all terraforming techs can get a PQ4 up to 20.

Occasionally there are random events that can increase the size of all planets in an area, or an individual planet. Very rarely that will happen more than once to the same planet, ending in a PQ72 planet. I've never seen this personally, but it has happened.

I had a mega-event that increased all planets quality up 20 levels.  This resulted in some highly humorous behavior from the AI, as we all were pretty much set and just warning now for an influence, domination, or alliance victory, when suddenly all worlds now have 20 more tiles to build on, and all the 'uninhabitable worlds' (which there were literally hundreds of, as I was playing the largest map with 'few' habitable worlds selected).

The AI just stopped fighting and bum-rushed colonies, sending them out en mass, to try and gobble up these worlds. I ended up going from making +400 / turn down to negative because building up my worlds faster than pouplation built up created a lot of 'in the red' planets for funds. 

This mega event only happened once to me, but I must say it was game-changing to the extreme, and not the way some are (as in the uber pirates are now here and you die - game over).  I had a hard-save just before this mega event and so reloaded and it didn't happen, so I had to resort to taking a save a few turns into the mega-event and then expirmenting that way, but in the end I managed to win just because I largely ignored the new planets and just focused on conquering.