contrib modules script policy?

Hello,

what is the backward compatibility policy regarding the contrib modules' uninstall scripts?

http://www.postgresql.org/docs/8.3/interactive/contrib.html

Can one be sure that all of the contrib module's functions etc. are removed from the database if you use an
uninstall-scriptfrom a newer server version? I checked the dblink uninstall scripts from the major versions 8.2, 8.3
and8.4 for example. There weren't any significant differences but I'd like to make sure. 

Could you tell me, please?

Thank you very much,

Peter
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