It's a neat series. It's interesting how it evolves, first from Alexandria then to Siscia.
1) Under the first tetrarchy the only distinction is Iovian or Herculean, so we have Alexandria issuing IOVI CONS CAES for both Diocletian and Galerius CAES, and HERCVLI VICTORI for both Maximianus and Constantius CAES.
2) Under the second tetrarchy, we still have the Iovian/Herculean distinction, but now also different types for the caesars, so at Alexandria Galerius gets IOVI, Constantius gets HERCVLI, Daia CAES gets CONCORD IMPERII and Severus CAES gets PERPETVITAS AVGG. All very tetrarchic!
3) Under the second tetrarchy, Siscia also starts issuing the full set of four types, but drops the Alexandrian Iovian/Herculean discipline and instead both augusti get both augustus reverses (IOVI, HERCVLI), and both caesars get both caesar reverses (CONCORDIA, PERPETVITAS). Siscia also tweaks the Alexandrian reverse legends slightly.
4) Under the third tetrarchy (post-Constantius) Siscia continues with same reverse type assignment logic, as appropriate to Severus AVG and Constantine CAES. The originally western PERPETVITAS type seems to have gone out of favor and Constantine predominantly gets CONCORDIA.
Here's my buddy Constantine, on a coin acquired long ago from the Beast mode Zach Beasley.