Thank you all for your prompt inputs. I had already booked two cruises back-to-back on QE, and in the absence of any enlightenment from the Q&A's, I hoped to tap on the wealth of regular Cunard cruisers on this forum.
We had cruised back-to-back on Azamara last year and the year before. On both occasions, were rewarded onboard credits for each cruise segment, amounts of which varies on the duration of each cruise segment. Details, and the process, are available in Azamara's website.
Similar rewards are also offered by some cruise lines too.