Of course! My current Membership Level is Platinum and it says that I have a total of 192 Total Nights credited toward elite membership, then it says 118 are nights stayed and 74 are bonus nights.
This information is found under my Current Account Summary / Membership Information; if I click on the plus sign next to "Nights Stayed" it opens a drop down that lists the nights stayed and bonus nights...
having the Marriott Visa Premier card gives you 15 bonus nights and any nights that you earned during the double nights promotion will show as well. Rollover kicks in when the total for all earned and bonus nights goes over 75, meaning that your Platinum renewal will rollover with those nights, as opposed to starting with zero nights.
Hope that explains the system.