I've assumed:
1. Satoshi mined almost alone from 1/3/2009 to 1/25/2010 (block 0 to block 36288).
A user, maria2.0, has proven she owns the private key of block 9455 (mined on 2009-04-01) by signing a message:
https://bitcointalk.org/index.php?topic=164569.0And she
claims to own "3.5 million coins between satoshi and her" (although that is probably false or an exxageration IMHO).