Looking over the responses so far, it becomes clear, in my opinion, that there are multiple ways to do this, so CORDELIANO, you should feel free to experiment and do what works for you.
That's one of my biggest philosophies of stage management, that you need to do what works for you. There's no one set way to do something, and (for the most part) no one set standard for paperwork or forms. You do what is best for you and the production.
I've done the musical prompt scripts different for different musicals, depending on the need of the show and my needs in calling the show, from putting the score into the libretto, to calling from the libretto, to adding in counts....it all was dependant on what i needed.
We all work by trial and error, even the experienced stage managers do. I learn new things about my job and how I can be a better stage manager almost every day...and i've found that to be the case for years! I hope it's always true for me!