Preferred IUPAC name of Protoporphyrin IX
I think both EPA and ChemSpider names are acceptable. However, I don't agree with dihydroporphyrin part in PubChem name. This is because the Gold Book gives following framework for porphyrin nucleus:



According to the numbering the IUPAC name of protoporphyrin IX is 3,3'-(7,12-Diethenyl-3,8,13,17-tetramethylporphyrin-2,18-diyl)dipropanoic acid. This name based on least locant numbers for ethynyl group, which have higher priority before methyl groups (3,3'- is based on positions of propanoic acid). The same name is given to protoporphyrin IX in Ref.2, without 3,3'- locants.

References:


IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.
IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN): Nomenclature of tetrapyrroles (Recommendations 1986); Prepared for publication by Gerard P. Moss, Queen Mary College, London, Eur. J. Biochem. 1988, 178(2), 277-328 (https://doi.org/10.1111/j.1432-1033.1988.tb14453.x) (PDF).