In theory, you could go to the Registrar Accreditation Agreement at
and read Section 3 (Registrar Obligations), then read the appendix for each tld, with the assumption that if there is no appendix for a tld, the icann rules apply.
tells you whether you are looking at the latest agreement.
In practice, the .com appendix doesn't seem to mention that they allow another set of contact information.
Does anyone know where the difference between .com and, say, .org is specified?