I've wondered the same thing. The bags, fairing and rack were all manufactured in the USA but were genuine accessories. Suzuki produced a brochure showcasing them.
The king/queen style seat was also a US manufacture but I've been told that the bike could be ordered off the showroom floor with the seat. I'd imagine that may also be the case with the backrest (and there a number of variations of that) but I haven't had anyone confirm it.
Sydney, Australia. The new leaner, trimmer shed: RE5M, RE5A, GSX1100EX, GL1800/Champion sidecar
These are the two versions of the backrest I have. The "S" logo badge matches the one on the accessory rack. The S backrest is NOS and came with a NOS T500 Rack that matches the RE5 Rack except for the mounts. Very odd they made it with the S and doesn't seem to have been sold as a RE5 accessory, Maybe it was sold as an accessory for a different model originally. Full page ad for Triple A is from a 1975 Magazine. The screw thru the logo sure seems crude.