The times are just estimates, afaik. Sometimes they come sooner than expected, sometimes later.
Yes if i recall sometimes the wait times are based on when a product is run.
For example, they make M60s one week, but then build M80s during another. Knowing that 5% of speakers (just an example value) might have a cosmetic fault they can say that they'll have Factory Outlet M60s ready in 2 weeks and M80s in 1, but if they had a good run and no M60s or M80s were faulted, you might have to wait for another M60s or M80s run to go around again.
Something to that effect.