So after doing a 'system restore' on my Ol' Faithful laptop, and reinstalling Chrome, my MMask extension was no longer there. Thankfully it's on mobile and I have the seed-phrase. The probs started when I attempted to reinstall MMask w the seed-phrase and same PW...now to my horror I have TWO MMask accounts (diff. Eth addresses) under the SAME seed-phrase and password. How is this even possible? I'd like to say the Eth address is the only thing differentiating the two accounts. But I can't think any further than that. Thx in advance.
now to my horror I have TWO MMask accounts (diff. Eth addresses) under the SAME seed-phrase and password. How is this even possible?
Metamask is an HD - Hierarchical Deterministic - wallet. In HD wallets you can derive multiple child keys from a single master key, which is represented by the seed phrase.
Each child key - a private key - represents a different child account, each with its own address.
What you're seeing is likely just the first two derived child addresses for your overall master key. If you want to use even more of the derived accounts, you can click the "Create Account" button in Metamask. Note that these accounts are always deterministically derived from your seed phrase, so your seed phrase is the only thing you need to keep safe (i.e. you don't need to save a bunch of different private keys).
For more on HD wallets, see: