Terry, you're making this sound alot more complicated than it really
is.

The 6-bit encoded part of a VDM sentence is simply a bitstream, packed
using a special code. Each character represents 6 bits of data from
0x00 ot 0x3F. It starts with the message ID (6 bits), repeat (2 bits),
MMSI (30 bits), etc. This is all defined in m.1371 and 61993-2, even if
it is a bit confusing at first.

The first 6 bits being a character and the message ID make it easy to
tell that the example string above is a message 1.