Ill clear it up. I do alot of mixing
When you mix records you get that person's base
If you mix with another freind who has the same base occupied, the first base will be deleted
If you register(save) freind A's base, the second base wont delete the first one and it just wont show up
You can have more than 10 bases in your game
You can only register(save) 10 bases
Basically, register the bases that are awesome so that they wont be deleted
And one more note of interest. If, for example, you mix with me, you will get all the bases that are in my game and I will get all the bases in your's.