under which situation my employer can apply for L1B blanket to L1A individual (instead of L1A blanket) category change?

My L1B blanket is expiring on 14th July 2017 but I94 is valid till Oct 2019. I am eligible for L1A and i am planning for individual L1A in premium processing to avoid travel outside USA for now. Can you pl suggest under which situation my employer can apply for L1B blanket to L1A individual (instead of L1A blanket) category change?

Thanks