Sure its definitely fine to repeat base and build, but the gains we see in Specialty we speak to pretty regularly! Specialty is a good thing! 
From ‘Training Plan Guide / Specialty Phase Training’:
“Research demonstrates, integrating specialization into a dedicated training phase spurs the human body to adapt specifically to the activities the individual participates in.”
and from ‘The Basics of Specialty Training’:
“Establishing base fitness paves the way for workloads that are heaped higher & higher during build training. With both forms of conditioning buttoned up, the intent is now to top off your fitness, uncover a high level of freshness and lock down your confidence over these final 8 weeks of training.”