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It might be A. sp. cf. "Gelbwangen Sichelbinden" that Dieter Bork pictures in the Aqualog Extra. It, too, came from an unknown collection site and exported from Manaus. Still, Frank is correct more photos in different moods will be helpful. Many of the regani-complex species appear very similar.
Dr. Stanley Weitzman, God rest his soul, was an immanent taxonomist and a 'lumper'. No one wanted to contradict his opinion. Now with genetic sequencing and all, we may see changes.
Is'nt it amazing how different the same fish can appear in different moods? I now am more certain that Frank's identification is correct. It is a form/population of A. cf. eunotus.
Your supplier can be the most reputable one around but no one is totally knowledgeable on every fish. Most, like...
You only need to look at the teeth on A. atahualpa (big, sharp ... and green). This is the fish that Dr Römer called "man-eater" because they would attack his hand whenever he put it in the tank. I've never kept the tetra so I can't recommend one way or the other, but I would error on the side...
First, Cruzeiro do Sul is located on the upper Rio Jurua. The Rio Moa, a tributary of the Jurua, is the type locality for A. moae. So that part seems ok. However all 'typical' eunotus-subcomplex species (= noticable split vertical bar(s) on caudal peduncle) are found in tributaries of the Rio...
It seems, from your description of their color, that the could be A. cf. eunotus (Orangeschwanz). This species is found around Iquitos, Peru and matches what you have described.
There are dozens of N. marginatus populations (probably different species). Take a look at TomC's site: https://www.tomc.no/fish.aspx?fishIndexID=1805&gruppeID=5.