Originally Posted by weaseltown

It's the former. Imagine that your back-to-back bookings get squished into a single master booking. So the one-time $100 property credit is applied to this one master booking and isn't repeated during your stay.

Certain promotions such as free night promotions already tend to have text that says the promotion can be repeated during a single stay. For example, say that the property is having a "stay 4 nights, only pay for 3" promotion. You can do a single booking of 8 nights and you'll only be charged for 6. There's no need to split the reservation up into two separate bookings to take advantage of repeated free night promos.

Some people attempt to skirt around back-to-back rules by booking a few nights with Amex FHR and a few nights with Chase LHRC, hoping to get back-to-back property credits. I wouldn't advise this because it's against the program terms of service, but you'll nevertheless see discussion of it on these forums. YMMV if you go this route, and don't be surprised if there are repercussions from the property.