Exactly,It depends if an extended lactation can fit your system. If you calving to fit a grass growth curve and want to dry everything off at Christmas, then probably not. If you're AYR calving anyway, and the cow is the type that can hold milk up, then crack on.
I remember a heifer back home on the robots that did 9,000L in her first 305 days, then another 9,000L in her second 305 days. She did get in calf eventually though. The next lactation was also 2 years, giving 12400 in her first 305 days (I forget what she did in the second but would have held up).
In a high input AYR calving herd, was she any less profitable than one that got in calf to calve on her anniversary?