In response to Paolo Cipola's ope-l 5257:
Of course, there's production of extra *surplus*-value. But it doesn't come
from the production of more *value.* Rather, it comes from the fact that the
worker in the more productive firm needs to work less to reproduce an
equivalent of the wage, but the working-day is not correspondingly reduced.
This is exactly what Marx says in the passage you quote:
"Nevertheless... the increased production of surplus value arises from the
curtailment of the necessary labor time, and from the corresponding
prolongation of the surplus labor".
Keep in mind that this is a chapter on the concept on the production of
*relative* surplus-value, more surplus-value without more value. Also that
the term "production" in "production of relative surplus-value" means only
that the curtailment of necessary labor-time "produces" the effect that a
greater share of the workday is surplus-time.
Andrew Kliman