Thanks so much for the replies! The info is helpful. Had noticed a few postings indicating having asked in advance for upgrades (from memory I think those requests were mainly for Hawaii hotels) & wasn't sure if this was a typical thing. Looks like it isn't.

Someone asked what I considered an upgrade to be & was mainly thinking along the lines of the concierge floor, a room with a good view or balcony, etc. From reading the posts on here for the past month or so, I've seen that suites are rare & certainly not part of the Marriott upgrade guarantee.

Thanks again!