That's not entirely correct because there are lowers for 7.62 x 39, 9mm, and .45ACP as well
Doesn't matter. If it is a correct AR-15 style lower receiver, then it will fit to any upper regardless.
I told the new me,
"Meet me at the bus station and hold a sign that reads: 'Today is the first day of the rest of your life.'"
But the old me met me with a sign that read: "Welcome back."
Who you are is not a function of where you are. -Off Minor