C&P doesn’t fall into certain inventory. Each hotel can offer as many, or few, or indeed no C&P rooms as they like. The difference is the payment the properties recieve from Marriott. With C&P the hotel receives more money than a plain redemption but unlike redemption there’s no possibility of a top-up if the hotel fills up. So if the hotel turns out full it ends up receiving just the agreed C&P rate which is a lot lower than they’d sell a room for, or the extra they’d receive from Marriott on a normal redemption. Basically SPGs C&P payment system was similar but SPG paid more to hotels for C&P, so for the Starwood hotels C&P was an attractive way to sell rooms, hence more SPG hotels offered C&P rates.