5milesbaby - I'm not sure that I completely understand your original post, so we might be talking at cross-purposes here, but on the charts I use (Jepp - used by most international airlines these days) the crossing heights that we are discussing are written in the following form: - EXPECT FL130 by Hazel,(or 130 at Nigit, or 140 40D before Lambourne etc etc) however actual levels will be given by ATC". No sign of a firm restriction there.
Secondly, your colleagues do not always give us these specific levels and points on the day - presumably depends on the traffic situation.
Thirdly, as the whole point of this thread testifies, sometimes they cancel them once further descent is given, sometimes they do not.
Fourthly, as a pilot I have absolutely no idea what your local agreements etc are - maybe the shorthaul guys who do 2 or 3 arrivals a day into LHR have worked them out through long familiarity, but I'm a longhaul pilot and I do a max of about 5 arrivals there a month.
As I said at the beginning, I hope I'm not talking at cross purposes to you.
t