A classic dozen (1,2,3), I have found missing for 31 spins, only once in a number of years of observing and writing live spins.
And 3-4 times missing for 29 spins.
However, by following 12 numbers ( any numbers), that don't show up during a new recording have gone missing 60 spins. Though that's rare, 12 any numbers can go missing 40 spins somewhat frequently. (if you don't specify those 12 numbers in advance).
That's not the case with the standard dozen, even if you follow the missing dozen.
The reason being is that there are 2 specific restrictions when it comes to following a missing dozen.
1. Wheel restriction: 12 numbers always occupying the same spot of the wheel.
2. Layout restriction: 12 numbers always occupying the same real estate on the layout.
That is y a dozen or column is excluded from the law of the thirds.