I created an extra anchor named center_lowered besides the existing center anchor in a base glyph. In the composite glyph I saw that the anchor icon appeared in the composite glyph, and when I clicked on it this new anchor could be selected even though the anchor only appears in the base glyph. It has something to do with naming because naming this center_lowered instead hellokitty it no longer triggered the anchor icon in the composite glyph.
I am finally getting to this. Creating new origin anchors like top_double works fine, but you cannot use new target anchors like _top_double. Why not? In my case I’d like to only have one top anchor in my base glyphs and all the messy anchors in the respective diacritics because the diacritics are all different and need individual placement of what would be a top_double anchor. The way it works now I would have to create alternate top_dieresis, top_macron, top_circumflex, &c. Very messy.