Tommy Tilt and others,
Nothing to do with IATA.
To be pedantic, I think that we are talking about two different procedures here:
1. The IATA In-Flight Broadcast Procedure (IFBP), part of which recommends broadcasting position reports at ETA -10mins on 126.9 and flying 1nm right of track; and
2. The ICAO SLOP as applied to the AFI region which allows for 1nm or 2nm right and allows the use of 126.9 to co-ordinate offsets amongst flight crew.
The IATA IFBP was implemented as a temporary(!) measure several years ago, due to the poor co-ordination between neighbouring ATS providers.
The ICAO SLOP as described in the WP13.pdf is part of the implementation of RVSM and is designed to
"enhance safety by reducing the risk of collision in case of loss of vertical separation".
I think that the paper (WP13) contained only the recommendations of a committee meeting which have not yet been officially adopted?
In any case, both procedures have the aim of increasing flight safety by reducing the risk of collision and I for one always implement the IATA IFBP, including the 1nm offset. I must admit that I wasn't aware of the ICAO SLOP within AFI, with its 1nm or 2nm option, until reading this thread. I do apply SLOP in NAT and WATRS airspace.
Live and learn!