Well, actually they added into the terms and conditions (this period for Renaissance and for Marriott it already said this for the last period and I think for the one b/f too) "Only one certificate per member." Now,whether or not this will work especially at diff. hotels, I would say you have a 95 % chance of success.

As far as being credited one night or two, I have been credited 2 nights all times (8) but one. This has been discussed many times already, but you're clearly supposed to be credited for both nights. This certificate is like a payment voucher or BB, so you're paying for the second night with this certificate. When I didn't get credited for the second night I saw on my receipt and the e-folio that they had written I had checked in on Friday and checked out on Saturday. They obviously had no idea how to process this, as was obvious when I gave it to them that they had never seen this certificate before (it was a miracle that they got it right- at least as far as not charging me for the 2nd night- w/o me having to go down there and make sure they would process it (I was always go to the front desk the 2nd night to make sure they'll do it right, rather than waiting till the next morning and have them fix up what they already messed up). I didn't do anything about it b/c I have already passed the 75 nights for this a month ago. And my chance for making PP (whatever the qualifications are) are pretty slim, although there is the lifetime count... Whatever...