I hold both B1 and B2 on a few types. Like a few guys in my company.
But, yes, people are rarely 100 % performent in both subjects.
I am for exemple 100 % b2, but still perform routine B1 work. If it comes to some complexe really B1 jobs, then I always ask for some advice from my B1 colleges. You just have to know your limits. It is almost impossible to know everything.
regards,
og