What are these "slots".
Flocsy,
I can't examine the bike in person but judging by the photos you've marked, I see these as reflections. Similar reflections appear longitudinally on the seatstay edges in the second-to-last photo in the original ad. This older Raven has the gloss black finish common at the time it was produced. On later versions, the black was a satin/matte finish and so had more of a luster than a shiny presentation.
As a hobbyist framebuilder and longtime enthusiast collector of lugs and framework and catalogs for same, I don't see this as a truly seamed eccentric shell -- because the inside must be smooth to contain and allow smooth adjustment of the eccentric insert. All modern eccentric shells I've seen are end-cuts from mandrel-formed, seamless tube stock. Some are split later to allow lands to be brazed on for a bolted clamp closure rather than grub screw retention of the eccentric insert. Some eccentric shells may be investment cast (rarer in my experience) and those may have a flat portion ("flats") to facilitate the later brazing-on of lands for the clamp-type closure of a split opening. I have seen exactly one of those and then only in a framebuilder's supply catalog decades ago. The third option is a seamless shell with some variation of a wedge eccentric, Bushnell's expander-type being the best in my experience.
Slot are generally regarded as longitudinal depressions below or through a surface. I see no evidence of that here. Flats are just that -- flat surfaces on an otherwise curved surface. Raised lands are flat surfaces that project or extend above the surrounding material. =If= those are flats or raised lands on this Raven, then they are placed laterally directly across the tube miter. This would be unusual in itself, but if that is the case it is a good place for them as the surrounding weld goes across those areas.
It is not something I would be concerned about.
Hopefully helpful, Dan.
