It doesn’t matter how many sessions you’ve observed, if you want to be a good coach you need to coach!
Observing sessions can help with your development, indeed it will help. Delivering a program someone else wrote will also contribute, but at the end of the day you need to practice designing your programs, implementing them, and then modifying them. And you need to do this for 10 years! (See rule 1).
Too many young coaches spend time observing the experts and then think they can coach (I also know some parents who do the same thing, but that’s another story).
Observing is passive. Implementing someone’s program is much the same. The real development occurs when making decisions. And then having consequences to those decisions.
When interviewing, I have always placed more emphasis on coaches who have run their own (less prestigious) program over those that have just observed/interned (even if it’s a more prestigious/higher level program).
Remember, good coaches aren’t necessarily the ones that know that most, they’re the ones that make the right decision at the right time.