"I just tried it and, yes, POPing into SBUF did work as expected."

So, Craig [1] just tried it on his particular hardware and got the result he expected.

Does this guarantee that it will always work for all targets?
Who knows?!

Is your application really that critical that it is essential to, say, POP directly to SBUF rather than via A?
If not, why take the risk?

[1] I'm not picking on Craig nor his hardware here; if we're going to trust anyone, I think Craig is probably a pretty safe bet!
But the principle is: if the Data Sheet doesn't guarantee it in black & white, don't make your product rely upon it!