As far as the trials shader goes it shows it so you know it exists to go get it because you can go get it every weekend but you can't get solstice shaders for 90% of the year so to display it would just be silly. Also the trials shader is only on adept weapons so it's pretty lame tbh
Even if the event is not running, it should appear in the API's collection tab, and shimmerfoil isn't even here, unlike other events or shaders that can't be earned anymore, while those two Osiris shaders actually appear in the API's collection tab, with a description and a source, while Shimmerfoil doesn't have either of them.
If they can't be earned then just like Shimmerfoil they shouldn't even be in the collection tab, and they also shouldn't appear on armors/weapons but should then be default shaders, just like DSC weapons use Cryptic legacy shader as default and GM weapons use Vizier Regalia as default shader too.