'Minor point but the runway is north / south not east / west (sorry, just like to be precise from time to time)'. Ha ha, well, with respect 02/20 is not north-south to be precise either!, is it?. Any way would be interested to know where the 'published' procedures are, perhaps as they are 'published' you would be kind enough to advise where?, I'd be interested to see them.
From your good self, 'the runway is not shorter'. Also from yourself, 'This does not effect take off as you start the take off roll at the start of the concrete, but if means that the landing zone is moved down the runway'. (Note you may not land on the runway in front of the piano keys, in normal circumstances). Therefore with a displaced landing threshold as you describe above, the runway is shorter for landing than it is for take off, correct?. Example for lez and to illustrate the above, taking off and landing in the same direction, same piece of tarmac:
total runway length 2000m
displaced landing threshold by 500m
landing runway available 1500m
take off runway available 2000m
do you concur gareth?