I have files with raw NMEA AIS messages that I need to decode to a delimited text format. Sample raw messages:

\\c:1581638400,n:24896*14\\$ANZDA,000000.00,14,02,2020,00,00*79

\\c:1581638400,n:24897*15\\!ANVDM,1,1,,A,15Nh=bP00hqWTC:E<3F<6Ign20Sd,0*1C

\\c:1581638401,n:24898*1B\\!ANVDO,1,1,,Y,E1IDWe0:aPQRg`94QRagV0W24W3tkNcA:UujH00000P020,4*09

\\c:1581638401,n:24899*1A\\!ANVDM,1,1,,B,15N8ct0P00IWliDE;UJpMOv42<1:,0*2C

\\c:1581638401,n:24900*1B\\!ANVDM,1,1,,B,15N3Ib?P01IWiupE<espU?v40D0t,0*6B

\\c:1581638401,n:24901*1A\\!ANVDM,1,1,,B,15O0JF?013qWbjPE;VwUKDP00<1C,0*3D

\\c:1581638402,n:24902*1A\\!ANVDO,1,1,,A,E1IDWe0:aPQRg`94QRagV0W24W3tkNcA:UujP00000uP20,4*4C

When I try to read the NMEA strings as AIS messages, the header isn't recognized by FME as a valid AIS message. The documentation lists the only acceptable message type headers as "!AIVDM" or "!AIVDO". I've been told the messages in my data are valid position reports, and they are correctly encoded within the framework of the NMEA standard. The "c:" and "n:" tags are prefixes placed by the AIS transponder that recorded the messages, and I don't think they have an impact on this (I've tried to run the file with and without the prefixes).

Has anyone successfully decoded any such NMEA messages with message type headers other than the two listed above? I already tried swapping out "!ANVDM" with "!AIVDM", but then the checksum bombs out.