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DOC 4444, (2015) - Possibly relevant extract..
8.7.3.4 The following distance-based wake turbulence separation minima shall be applied to aircraft being provided with an ATS surveillance service in the approach and departure phases of flight in the circumstances given in 8.7.3.4.1.
HEAVY / HEAVY 7.4 km (4.0 NM)
HEAVY / MEDIUM 9.3 km (5.0 NM)
HEAVY / LIGHT 11.1 km (6.0 NM)
MEDIUM / LIGHT 9.3 km (5.0 NM)
8.7.3.4.1 The minima set out in 8.7.3.4 shall be applied when:
b) both aircraft are using the same runway, or parallel runways separated by less than 760 m (2 500 ft);
It refers to the "approach and departure phases".
My guess - some individual countries might include Landing and Take-off in these phases whilst other countries might not.
Although why distance is universally accepted for landing (where radar is used) but not for take-off beats me..... Anyone have an explanation ?