I know this is an old topic, but NSU-Fiat and Neckar-Fiat is confusing. I've been collecting badges for Fiat, branching into non-Italian builders.
NSU sold their new German (Heilbron) plant to Fiat due to financial problems. In 1957 NSU decided to build cars again, so asked Fiat for their name back. NSU-Fiat neo-Fiats were built 1929 to 1957 (and maybe 1958). I say "neo" because though they bought rights to build from Fiat, they often improved/changed the line. Most agree Neckar built a superior product, to the Italian models. I think it was in 1959 when the new Neckar (the 1100?) came out. They stopped production in 1971 because of "high labor costs" and Fiat wouldn't sell them rights to the latest models.
A lot of sites repeat what they saw on other sites, possibly because the dealers encouraged the "error". (The NSU Prinz was noted for reliability.) BTW, the Neckar name comes from a nearby river. Names are further confused. e.g. the 1959 Fiat 1100 was known as the Europa when built by Neckar, though either name works.
