Most of the articles that appeared in the 1970s US gun magazines were based on a few demo guns that Mauser prepared before official production began. These demos are usually just reworked and camoflaged Swiss lugers
Mauser did indeed make both the Parabellum and the HSc, although the HSc parts were almost completely made at Manurhin in France.
If you are going after a collectible Parabellum American Eagle, the main tips are:
-As unfired and complete as possible (gun, box, 2 mags, rod, takedown key, target, manual).
-As low a serial number as possible.
-Look for the proof, an Eagle/N proof on a PAE is rare, the FBM is the common one.
-Alternatively, look for the transitional 1972 model with Swiss style small parts and the P08 style grip.