Hi Tony
My perception is that the Seydel 1847 coverplates are not the same as the Hohner 150th Anniversary Standard Edition's. The Anniversary seems to be a re-emblamed Big River. If you have a Big River in your arsenal, compare it with your 1847s and you'll notice the 1847's 'higher' and shorter-radius 'ramp', absence of side 'vents', different back design, and longer dimensions to accomodate the wider hole spacing.
Does one company make covers for the other? I don't know.
The Big Rivers have been around for a number years and have very nice coverplates, indeed. Perhaps Seydel chose to encorporate some of the the BR's better qualities, while improving on the rest.
Cheers, Staggerin' Jim Listen to Roots Harmonica at http://www.live365.com/stations/staggerinjim