Why don't using Permanent Identifier on QC certificates?

[Juan Carlos Pérez Aguayo <juancarlos.perez@xxxxxxxxxx>]

In the QC draft is stated:

"...The serialNumber attribute type SHALL, when present, be used to
   differentiate between names where the subject field would otherwise
   be identical.  This attribute has no defined semantics beyond
   ensuring uniqueness of subject names.  It MAY contain a number or
   code assigned by the CA or an identifier assigned by a government or
   civil authority.  It is the CA's responsibility to ensure that the
   serialNumber is sufficient to resolve any subject name collisions..."

and on the Permanet Identifier drfat;
Sorry if this discussion has happened before, but I don't know if there are
some final statement:

"... A serialNumber attribute may be used for two
   different purposes in the DN of a person:

   1) In a DN or a SubjectAltName to differentiate between
      two names (for two different individuals) that otherwise
      would not be different.

   2) In the identifier field from a permanent identifier.
      This is the recommended use for national ID's and
      employee ID's, for example. ..."

Now, consider this:

a person has a unique identifier, assigned by a goverment authority, wich is
guaranteed to be unique on a national scope (country domain)

How to incorporate this identifier into a certificate?.

SerialNumber or SubjevctAltname field? When I read the QC profile
"..identifier assigned by a goverment o civil authority...", and then the PI
draft say "... This is recommended use for national ID's...", I am confused.

Why the QC does not use Permanent Identifier?

Thera are some application wich need incorporate this class of personal
identifier. By example, in my country (CHILE) each people ha an unique ID
stamped in a card (this card has the photography and handwritting too), and
this is broadly recognized for identification. One can to do many
transactions wich need this ID for proceed.

Thanks in advance

Juan Carlos Pérez A.
Acepta.com