A. I do not agree that any wage labour under capitalism can be
adequately characterised as u-P just on the grounds of the kind of
use-value that its commodity product has (just so it has one).
B. The 'closeness' of the Labour to the final act of mere exchnage
(sale) is irrelevant.
C. It is labour, not 'functions' that are the object of the
distinction.
D. The question of the degree of vertical integration, the extent of
'contracting out' or whatever is not germane to the issue.
E. IMO, The only sustainable basis for a distinction is that u-P
labour does not produce a commodity, because it is not performed
under capitalist direct relations of production (eg domestic labour,
non-commodity producing state labour).