Not sure whether this helps: $contentobject->versions() returns an array with all available contentobjectversions of $contentobject.
If you just need to know how many versions an object can have you need to check the content.ini, as this is set there.
As you seem to work quite a lot with PHP code you should check the file \kernel\classes\ezcontentobject.php and read over the function names to get an idea what is available there. Usually the code is quite good to understand.
Claudia
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