PCs are a lot less likely end up on the Ethereal plane unexpectedly compared to the Astral:
- Flung into the depths of the Ethereal plane by a Vanish spell (objects only)
- Plane Shift: Used to move an opponent to the Ethereal
- Breaking a Staff of the Magi has a 50% chance of sending the mage to another plane of existence
- Forced to regain physical form inside an existing object because a particular spell or potion has expired or a Dispel Magic has been cast upon the traveler
- If Blink places the caster in a solid object, and a second check still places them within a solid object
- Oil of Etherealness
However, having put together the information earlier on the Astral plane, it only made sense to go ahead and apply the same treatment to the Ethereal plane. Having already worked through the Astral, I had a template of what information might be missing (or contradictory). Using that, I did my best to resolve everything as close as possible to the 1e AD&D context.