I have two minecraft accounts which I use on one computer.
When I play in any world as my main character, after I log out of minecraft and sign in again with my secondary account (for map testing), I'm still playing as my main character in the same location with same inventory, skin, etc.

No matter how many times I login on minecraft as my first or second account, I only play as my first one. But player data is created for the account I intended to play as.