MPLS DRAFTS EXPIRY and ITS RULES.

[SRIRAM]

Hi all,
Can anybody help for that, can any drafts with different numbers can have
same EXPIRY DATE from .
But it does, draft-ietf-mpls-ldp-09.txt and draft-ietf-mpls-ldp-11.txt.
Is there any rules pertaining to the expiry dates of drafts.
Kindly reply.
Thanx in advance.
Regards
-SRIRAM