In Oz we had an 'agreement' that those that could (domestic anyhow) would descend at cruise into 300K. Our major airline decided one day to bump up the cost index and not tell us, just all of a sudden they were doing anywhere between 260 and 300K. Nobody died, but the sequences looked crap until somebody asked a pilot what was happening, "What? Nobody told you!" was the response
After it all settled down the result has been that everybody is treated the same: if you want somebody to go fast you explain it patiently and comprehensively, or, if they are 'profile' you assume 280 and: slow them down if they exceed expectations inconveniently, or, leave holes in the sequence and shaft everybody if the reverse is true.