There was this period from about 2003 through 2014 when I was writing a novel a year for each of Ace (part of Penguin) and Tor (part of Macmillan). Totally different orgs and pub dates were skewed by about 6 months.

So why did I regularly get sent copy edits and page proofs to check for both publishers SIMULTANEOUSLY WITH THE SAME DEADLINE?

(I'm certain they were conspiring to stress me out!)