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Having read a fair bit on the debate about rotation curves. Just for the record I'll go forward assuming the following from a definitions perspective, (unless anyone howls me down):
i) the Rotation Curves (RCs) of the most luminous spirals decline at large Radius (R), they are typically also not dominated by Dark Matter (DM) at these radii (by definition);
ii) similarly, dwarf galaxies have rising RCs at large R (not flat). This is still a problem, and also the dwarfs, typically, are not spirals;
iii) the actual OBSERVED RCs that are deemed to be DM dominated, and decline, seem to be very rare. So while it may not be precisely correct (in detail), it would seem in general, that a flat RC still approximately describes the behavior of the observed mass distributions of spiral galaxies at large radii.
... just for the record.
Cheers & Rgds.
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