A primary ( free) amine test will indicate the presence of a wide range of primary amines (e.g. MDA, PMA, amphetamine etc,).
A secondary amine test such as Simons Reagent will indicate the presence of PMMA, Meth, MDEA, MDMA etc, but - as with the results from a non-specific primary amine test when more than one primary amine is present- Simons reagent will also give an indistinguishable positive result if a mixture of secondary amines is present.
Amine tests should always be used in combination with other reagents such as Marquis or Mandelin, but even these reagent combinations cannot indicate all possible combinations of drugs.
Take a mixture of PMA & MDA, or say a mixture of PMA and MDEA. The former would likely appear as MDA, due to the darker colour produced by Mandelin and Marquis with MDA. The later mixture, if tested with all the above reagents, would likely indicate MDA & MDMA, again because the darker colours dominate.