First, about the rules: I’ve always thought it was six packages per six months (rather than per year). One of the items @Icon posted above says …
Unfortunately the link above is dead; this page seems to have the same information:
https://law-out.mof.gov.tw/EngLawContent.aspx?Type=C&id=129
Second, about enforcement: I’ve asked a few times on this site about if anyone’s ever been stuck with extra payment on the 7th+ shipment. No one has ever said yes. So I’m not entirely sure if this rule matters anyway.
I’ve always assumed that it was six packages per half-year (i.e. Jan-June, then a new period starts July-Dec), and that the count starts over in July, but perhaps that assumption wasn’t justified - maybe it’s six packages within the most recent six months. When did your first Amazon orders arrive? If they were at the beginning of January, I think you’re totally safe. But if you want to be extra-careful, wait until it’s more than six months since your first Amazon order.
Side point: if you’re trying to make use of iHerb’s current discount on orders over USD$80, remember that if you’re over that amount, you’re supposed to get hit by customs duties anyway.