The Spirit Realm

Does Knowledge of the past and Taelosian guard, the hp regeneration part does not stack looking at lucy, but can you have both buff on at same time, thus having mana regen and overhaste?

You can have both on at same time yes

Stacking issues were changed sometime during 2009, they never used to stack but a conscious decision was made on the parts of the developers to change that (which occurred around the time that all the clickies were added to SoD gear). All that said, Lucy shows no stacking conflicts between these two spells because there are no conflicts. The only thing I can think of was that perhaps you looked up Knowledge of the Past and noticed the conflict with Aura of Taelosia.

Thanks guys, it is good to know.