A word of warning based on a bad experience.
I am not a Abound owner and did add my bonvoy number on marriott.com for a previous II getaway at an Abound property. I did not verify my bonvoy number was on my reservation when I checked in, and I subsequently checked out without it being tied to the reservation (not sure how it was not there automatically, but i digress).
I opened a missed stay with bonvoy for the incidental charges, and was told I was not eligible unless i was an Abound member . When I pressed them, the rep threatened to audit my account and remove points for any credits i had ever gotten thru Interval. Their rational was that they had proof that my reservation was not thru Marriott.com and that i should never get any credits for anything since i was not an owner (or had booked thru marriott.com). I let it drop as we did not spend much while onsite.
In this case, me tying my bonvoy number to the Interval getaway backfired on me. If i had been an Abound member, they would have fixed it - but since i was not they denied me because the reservation was not made thru marriott.com.
I have always gotten credits for Interval stays when I make sure on checkin that they have/add my bonvoy number. Those credits include incidentals and usually a check in bonus. So i plan to continue adding my bonvoy number while onsite instead of adding it on marriott.com ahead of time.