My NMS installation receives updates daily sometimes more via GOG galaxy but the version number 1.77 never increases. Is that normal ?
Not typical behaviour, certainly. Haven't seen anything like that here. Have you run the Verify / Repair option under Manage installation?
The current release version on GOG is 1.77_GOG_MP vice the unadorned 1.77. Your symptoms could be explained by something (anti-virus software?) blocking the update to the MP version which causes the updater to repeatedly attempt to install the newer one. The MP release might
want to hook into networking code that earlier updates didn't touch and that may be viewed as suspicious by the AV software.