Actually the Platinum guar states that you are to get $100 US - not Marriott bucks - but hard US cash. They should have given it to you when you told them on check out that you did not get it.
Sometimes, I have not gotten it when I have changed rooms at check in (the gift was wtg in my preassigned room) - and in that case I tell them right then (and they give me the water/cookies in a bag). That really isn't in the spirit in my mind - I changed rooms - not their fault.
But in your case - they should have said - "I am sorry we didn't fill our promise of service" and given you $100. The Mgr might need to be called - but you a) shouldn't have to tell them what their policy is and b) should have had an immediate call from the GM/Mgr on duty - not have to wait.
As it stands - you prob won't get anything now.

(I am not saying you aren't entitled or shouldn't) just that with the days that have passed, there is doubtfully any record of whether you did or didn't and the memories have faded.
You should have contacted the GM that day if there was no mgr on duty to talk to at check out. Next time, get the name of the front desk staff, ask to speak to the mgr, or leave your business card and haev that person contact you. Or ask for the $100 us cash - that is the Plat guar and Marriotts policy. Have them pull it up on the web OR call Plat MR cust service right then, while you are at the desk.
MSP Flyer