Elderling Creations Theory (Spoilers through all the books and Dragon Haven)

[Mervi]

WHY, for an example, didn't Etta's skull quicken? She certainly had worn it for a lot longer than Kennit had worn his charm.

If by quickening you mean that it didn't work to prevent her pregnancy, she removed it after talking about it with Bolt, right?. Or do you mean that it never spoke to her like Kennit's charm did? I always got the impression that these contraceptive charms were REALLY tiny, like the size of a navel ring, so they weren't supposed to quicken/talk anyway.