Understanding the $tau$ Branching Fractions from PDG

Of course they do not add up to unity when they are inclusive states, there will be overlaps where the same channels will fulfill the "larger or equal " criteria.

The probability will sum up to one of all decays are identified with specific number and type of particle . These are the ratios after before $Γ_{11}$ and after $Γ_{18}$, those without "less than or equal" signs in your link. Their summation will always be less than 1.

Copying from comment by Martino :

They actually explain what they do here, but it's a little bit technical.