Here's what the Terms and Conditions say:
2.1.d. Qualifying Stay [Section Title]
iii. Members cannot earn or receive benefits at multiple Participating Properties for the same stay date(s).
Source:
https://www.marriott.com/loyalty/terms/default.mi#earn
In reality, whether you get points and/or elite night credits for both stays will depend on what happens behind-the-scenes. That's why you see two different responses with two different outcomes.
Originally Posted by
RobOnLI
Do I jeopardize my earnings for the monthly stays by having intermediate short stays in the same time period?
I usually take a "strict interpretation" of the terms and conditions of travel programs. But this scenario is one in which I'd have no qualms in doing myself. The only way to get the benefits you earned is to include your membership number on that second reservation. And no hotel group is going to kick you out of their program because you provided them double business on certain nights of the year.
Worst case scenario is that the points for that shorter weekend stay won't get posted. Although the most likely outcome is that you'll get points for both stays but only elite night credits for the longer stay.