I;m not totally sure, but I'm pretty sure their age and corrected age is still taken into accound, even up to about 12-18+ months, depending on how premature they were. For example, a micro premmie born at 27 week will be monitored for alot longer than a bub born at 35 weeks. But yep, I'm pretty sure bubs are taken for their corrected age rather than their 'birth' age for a fair while, iykwim.
Not sure about the development side of things tho, I guess that would also depend ont he prematurity of the baby tho.