SLOP is a recommended procedure in NAT MNPS airspace, formalised a year or 2 ago by NOTAM from the various countries who control bits of the NAT MNPS.
2mile right offset in Africa is an ICAO recommendation published 8 to 10 years ago (sorry, not sad enough to have the doc reference) and used by anyone with an ounce of sense and even the vaguest desire to draw their pension for many years before that. My company publishes it as a company SOP in our Ops Manual.
Like someone else said - if you don't do it in Africa you need your head read, even if you can't find it in black and white.
Basically they're the same thing.