Thanks Rainer, yes, I've just opened the cutting edge version and they are there. Somehow when cliecking on Cham, the main pane shows all the glyphs from all the subcategories, but Tham doesn't show them.
When having a little time I'll tidy up my XMLs and put them on GitHub. I don't tend to populate the accents field, as almost any marks can appear on any base, so a) it's not very helpful trying to specify if we're specifying everything — that's not what specifying is; and b) Glyphs uses this info to make mark clouds, which for me are useless (never used them), especially if there are hundreds of overlaid marks. And anyway, now we have the mark preview plugin that shows mark positions individually.
I think the sidebar entries should be alphabetised: Cham, Khmer, Lao, Myanmar, Thai, Tham.
@RobPratley Perhaps 17A3, 17A4, 17B4, 17B5 and potentially 17D8 should be moved into a new category 'Deprecated'. Chapter 16 of the Unicode book (p639) advises not to use them. Alternatively, if we want to keep them in the existing categories, I'd put 17A3 after 17A2 in the consonants section, 17A4 in with the ligatures, 17B4-5 in with the vowels and marks, and 17D8 with punctuation.