First systems with lilypond-book-preamble.ly

[Urs Liska]

Hi list,

if I include lilypond-book-preamble.ly Lilypond outputs the systems 
individually and cropped.
In my first tests I saw that the first two systems are the 
bookTitleMarkup and the scoreTitleMarkup.

Can I assume that this is always the case. I.e. can I assume that the 
third system is actually the first music system?
(I have to know that because I want to include the systems in a text 
document with a loop and would just start this loop with the third 
system if my assumption is correct).

Best
Urs