There is an amendment dated 12 May 2004. It can be downloaded
here and will give you the cold hard truth as you call it.
The definition of acclimatised in the amendment states:
'Acclimatised'
When a crew member has spent 3 consecutive local nights on the ground within a time zone which is 2 hours wide, and is able to take uninterrupted nights sleep. The crew member will remain acclimatised thereafter until a duty period finishes at a place where local time differs by more than 2 hours from that at the point of departure.
As far as I can see that is the same as the definition in the Jan 2004 version.