LordAO said:
There is nothing that says undead have to be evil, just most are. And there are good liches!
I see you haven't read the description of liches recently. I quote from the Monster Manual, Pg 217:
"Alignment: any evil"
and
"The process of becoming a lich is unspeakably evil..."
Maybe not all undead need to be evil, but liches are supposed to be.
The fact that the core rules and the FR books were written by the same company does not mean that they are all "as official" in all cases. If they had wanted the rules used in the Forgotten Realms to be "standard", they would have put them into the core rules in the first place. The fact that they are provided in separate books means that the authors/publishers intend a separation between them.
There is nothing wrong with having a particular game setting contradict the core rules. However, you must accept that said contradiction is only applicable in that setting. The rules in the FRCS and Monsters of Faerun are used in the Realms, but do not apply elsewhere.
So, there are variant liches in Monsters of Faerun. Fine. They can use the Clone spell. Maybe all liches in FR can use clone. Don't try to extrapolate that back to all of D&D, though. The same rules simply don't apply.
Heck, even if the Baelnorn were in the core, it is not wise to generalize from one aberrant case. There are rules. There are exceptions to those rules. The exception does not then imply that the original rule does not exist.