What should I tell someone so they can restore my bitcoin from a seed in 20 years? I'm making a metal backup of my bitcoin wallet. It's tedious to do by hand, so I want to add the right info but not to much. This is my current idea, I want someone else to understand it 20 years from now, if i'm dead. This is what i've come up with so far.

Seed:

This is a wallet seed generated with a Trezor wallet in 2017 using bip39. 
It can be used to get access to bitcoin. Keep it Safe.


Pass-phrcace (on other location):

This is a wallet seed passphrace generated with a Trezor wallet in
2017, using bip39. Use it with a wallet seed stamped on a similar plate.
It can be used to get access to bitcoin, Ethereum and Litecoin and maybe 
other currencies.
Keep it Safe.


The bitcoin seed will contain a small amount of bitcoin and the most will be decrypted with the passphrase.

I'll probably attatch the bip39 specc on paper aswell(anything else) but that might burn up or whatnot so the vital info should be in the metal-stamp.
You probably can get that engraved or something since its a general background information. 

But if you do not have the room or want to stamp that much, you could probably get away with a few key words such as wallet recovery seed, trezor, BIP39, etc. One could search those few terms and find out what it's for. Although, it is a bit of a security risk if a random person finds it.