This is a short list of period named papers that may be of use when determining photo authenticity.

Gevaert Ridax: also seen just as "Ridax" was a Belgian produced photo paper.

Agfa Lupex: may also be seen as just "Agfa".  Agfa is also a post war marking.  Agfa Lupex is the pre-war and wartime marking.  It was German produced.

Agfa Brovira: may also be seen just as "Brovira".  Note, a lot of photos exist from the 1950's that were developed on Agfa Brovira paper.  These were left over war time stocks of which many existed. A typical scenario is where the soldier takes photos during the war and does not have them developed until years later.  

Agfa Brovira is still manufactured, but is renamed "Agfa Brovira Speed".  It is German produced.

Leonar. German produced.

Mimosa. German produced.

Velox.  pre-war manufacturer.

Selo.  British produced and exported pre-war.  So don't think it's odd if you find period photos of German soldiers on this paper.

Toke note that not all original photo papers will yellow with age. The higher gloss papers retain their whiteness quite well.  It is the satin and matt finishes that yellow noticeably.