You'd think AMD would say over 60m consoles if the XB1 was at 20m+. We know that the PS4 is at 40m and we know that the XB1 has easily sold more than 10m:

Do they know how many consoles have been sold to consumers?

Only the PS4 which is at 40m sold through.

More like under 10 million

I meant AMD, why would they know how many Xboxes are sold.

Anywhere from 19 to 21 sounds reasonable. Without any solid numbers anywhere, it's really hard to say how well the console is doing, aside from saying it's obviously getting drubbed by the ps4 in most countries. AMD might just have been rounding to 50+ because the people attending their conference don't much care about the difference between 50 and 60 (as opposed to say, the difference between 50 and 100). 

EDIT: AMD wouldn't necessarily know how many Xboxes have been sold, but they definitely know how many have been built, since MS uses their parts to manufacture the console. 

We've gotten different numbers from different sources, I really wouldn't put much weight to this. "Over 50 million" could easily mean 60 million. They just don't care all that much to be completely precise because it doesn't matter.

Over 50 million can mean lots of things. Its pretty much confirmed at this point that the XB1 is over 20 million (with all the sources saying it).

No, not really. We can't be 100% sure MS has sold over 20 million consoles, but we do know they aren't doing that bad.

I'm sure they know how many chips sets they've produced and sold. We know the PS4 has sold over 40m which leaves the rest for the XB1. If it was 20m then surely they'd say 'over 60m'. No?