and, reading further, from
ISO/IEC 9594-6
Informtion Technology...
Part 6:Selected Attribute Types
...
6.2.1 Case Exact String
...For two strings...to match for equality, the strings must be
the same length and corresponding characters must be identical.
A Printable String can be compared with a T.61 String: where the
corresponding characters are both in the Printable String character
set then comparison proceeds as normal. However, if the character
in the T.61 String is not in the Printable String character set then
matching fails.
6.2.2 Case Ignore String
... rules for matching are identical to those for Case Exact String
attribute syntax, except that ...
... this seems to cover the cases you mention. Now, what about if
you only have "abstract data" and need to reconstruct the signature?
I always thought the directory would let you encode it either way
if you could (it seems to be generous like that), with no definition
of preferred. It seems you can sign either, and for verification can't
reject a signature merely because the received encoding wasn't the one
signed...
yuck.
Why don't you like a "use Printable String where you can" rule? It sounds
like a defect to 9594-8 to me.