Edit: question has already been answered in February 2012 here: http://www.leeduser.com/credit/CI-2009/EAp2
Didn't find it before, sorry for any confusion.

Dear all,
on several spots in the Ref Guide it is said "project teams wishing to use ASHRAE approved Addenda for the purpose of this credit may do so at their discretion. Addenda must be applied consistently across all LEED credits".
This means that project teams may use single addenda to the standard as long as they use it on all credits. they do not have to follow all addenda published for that standard. Is that correct?
Thanks in advance!