Hi, Thank you for clarification.
But I still not understand something.
You said for gallery it use native WP post attachments.
Do we need to add any meta to this attachment?
Because when I see this part in your plugin:
Adverts_Gallery_Helper->load_attachments()
It seems to only load attachment if it contains certain meta in it.
Will it work if we just use importer plugin? (they will not add this meta to attachment)
If it wont work, What all the meta needs to exist in the image attachment?