I think I see a hallmark so the 18k may be legit. The only way to know for sure is to get photos of the reference number and movement. The OVD isn't 100% accurate and there were a bunch of different dials.
Gold plated versions usually have stainless steel backs. Yours has a hallmarked gold back, so I'd guess the whole case is gold.
The vintage database is full of inconsistancies.