Can I accumulate PV across multiple orders (cumulatively)?

Yes, for coupons and promotions, PV are calculated cumulatively over a period, not necessarily from a single order. However, to qualify for personal activity, each individual order must contain at least 20 PV (in some countries — 10 PV). This means two orders of 10 PV each will not grant personal activity in countries with a 20 PV threshold — a single order of at least 20 PV is required.