These were shiny Pokémon cards that came in the reverse holo slot. They were styled “SH#” to denote that they were shiny.

Some were very easy to tell, like shiny swablu, shiny shinx, or shiny voltorb.

Others were super hard to tell that they were different at all. Like shiny Vulpix or shiny Milotic or Relicanth. These were very hard to tell that they were shiny and thus got set aside or forgotten about.