I just ran the e -commerce updater to update the GTN 750 to 2.5.16.1, but when I start the GTN in the aircraft, the initial screen just says 2.5.16 is this correct?

Hi,

yes this is correct, the version number displays only the first three digits. The last digit is really a 'point' release with a small fix to something which went through with the release (literally 1 line of code in this case). You can manually cross check the win.xpl plugin file version number to make sure (this is a dll renamed xpl, right click, properties, details)