Lee,
Thank you for you inquiry.
Unfortunately there is no "automatic" method to determine if the chart file contained on the SD/micro-SD/or HDD within the TZT, TZT2, or NN3D unit is the latest & most up to date.
However, looking at the example of the MM3-FNA-022;
looking at the CATALOG menu within the unit itself I can determine that this chart file is SDNA022FISHMAP01.DBB.
If I then visit the FurunoUSA.com website, I can find the MM3-FNA-022 & click on the MapMedia link at the bottom of the page. From the MapMedia page I can see that the file name for this chart is the exact same SDNA022FISHMAP01.DBB as what is already in my TZT, TZT2, or NN3D and as such I can determine the chart in my unit IS the most current & up to date. If the file names do not match it is likely that you simply have a previous version of the chart file. If so the data can be downloaded from the MapMedia site and copied onto the SD/micro SD card of the unit.