"And I don't understand why you say that DADGBD is "essentially standard tuning"?"
Because it is essentially standard tuning. I'd never ask for a chord chart for drop-D tuning. It's pretty well understood that every chord you play in standard, you play in drop-D with a compensation for the lower bass string.
Same goes for double-drop-d. Every chord you play in standard, you play in double-drop-d the same way with the high E string covered two frets higher or muted. with the greatest respect,I think you are missing the point of this tuning,the point as I understand it,is to enable the guitarist,to get some of the modal sounds that are difficult and sometimes impossible in standard tuning,much as one would in DADGAD. However I find it more useful than DADGAD,because I can retune to standard or drop d much quicker,I might often plan my sets,so that I play something in standard,then drop D then double drop D,getting contrasting guitar sound,however each to their own.