Multiple OpenPGP messages per file: legal or not?

I've hit an interoperability problem with GnuPG, and need guidance on
the legality or otherwise of multiple OpenPGP messages in a single
file where those messages are "Encrypted Messages" (as defined in
Section 11.3 "OpenPGP Messages".

If I have a file which contains 2 Encrypted Messages, e.g. the packet
sequence goes:

ESK Sequence | Encrypted Data | ESK Sequence | Encrypted Data

is this:

a) legal

b) illegal

c) legal but not supported by GnuPG

d) outwith the scope of the ID since that defines only "OpenPGP
Message Format", not what you can do with those messages

I believe the answer is either (c) or (d)....

Rachel