I installed from the manual download before realizing that Galaxy is needed for uploading discoveries with your account name instead of Explorer. I then installed Galaxy and manually added the game to it.
Now when I run the game it does list my name, but none of the achievements are showing in Galaxy, is this a bug?
Also will all my older discoveries always be by Explorer?

i was wondering the same....?

This is years old and I'm reviving it... I had the same thing happen just a couple days ago when I discovered the same thing. I have over 70 hours of original play from before installing Galaxy - how do I get those achievements to show up in GOG?

You could try uninstalling the stand-alone game and installing anew from Galaxy. Backup your saves before trying this!

Are you getting new achievements to show up in Galaxy? If so, it may be that the Galaxy achievement only triggers when the event happens and so won't be recognised after the fact. An option, assuming you're getting new achievements recorded, is to soldier on and figure that you'll pick them up on a new start someday. I currently have two "threads" active, the older one is in the Eissentam galaxy; it was started fresh when NEXT went live. I started the second to have a game in Euclid to be able to portal travel to the Community Event planets after the main mission completed.

This is exactly it. Achievements are not retroactive.

The discoveries will always be listed under the name you had at the point of discovery. Just be glad you did not made your forum user "MommasPhatA$$" before discovering that NMS abuses your GoG name as your characters name in game ;)

When I fire up Galaxy once in a blue moon the achievements done in the time between do update. But I did the manual install from the installer I downloaded via galaxy, not the browser.

edit:
HOLY NECRO! oO

... *sigh*

When I expand to Show All achievements, I see percentages of completion for all, except one which I attained 2 days ago (after installing Galaxy) got updated and is only 8.1%. I'm guessing since I haven't completed any of them before installing Galaxy, as I progress they will pop up in Galaxy like The Forever War one I just got. Contact is 57.9% atm, my biggest achievement thus far.

i think these percent(%) by individual achievement means how many users of this game got that achievement, so the smaller the % - the cooler is achievement. and that % on the top shows how much % of all achievements you got
my current best one is : A scanner darkly , uncommon 17,6% got it two years ago (it means that 17,6 % of people playing this game got it)
My current total % of achievements is 51% (14 of 27)
the best posible achievement would be: To Live Forever , Legendary 0,1% (to reach center of galaxy in permadeath mode)