I remember having a (pre-8/18) stay where I used a cert for one night and paid cash for the rest of the stay, and did receive points for the cash nights. The cert and cash nights were under 2 separate reservations.

You did forget to factor in one thing: if you reserve 4 nights on points, you're eligible to get a 5th night free. So those 70,000 points could get you 5 nights rather than 4 - and conversely, if you can't / don't want to stay a 5th night, it's a waste of points if you can use them later for a 5-night stay.