M03f referred to M03 messages, which started and ended with a quintuple-digit-group (e.g. "33333"), but after the message groups there was the amount of groups in the message padded out with zeroes, repeated twice, which was not included in the amount of groups provided in the preamble. In practice, however, this variant was only noted on one message, with ID "886/71", sent throughout late August and early September in 2007.
The aforementioned message started with the group "33333", and ended with the groups "33333 00071 00071". This same message was also transmitted by E11a.