Neighbor->ago and Fix->(min)_pre_exchange()

Dear developers,

do I understand correctly that
EVERY time re-neighboring and/or movement of atoms from processor to processor
occurs, appropriate methods of fixes are called: Fix->(min_)pre_exchange() ?

Is there any other event possible when neighbor lists are changed and those
changes are not 'seen' by pre_exchange() function?

At some point during re-neighboring, Neighbor->ago is probably reseted to zero?

Kind regards,
Denis.