That was actually one of the first things I've tried. To my surprise, GameStop kept asking me to register before it would allow me to update (there is of course, no register option to be found anywhere within the GameStop app for Sins). My original thought was exactly what you've said previously.. I registered my retail copy the day I bought the Entrenchment DLC because Impulse would prompt me to do so before I downloaded the DLC. So theoretically, GameStop should already have my Sins registered.
Here's my original post within another thread here on the technical forum:
"I bought my retail copy of Sins back when it first came out, and also the Entrenchment DLC as soon as that was released.
It's been years since I've played Sins. Now that I bought a new PC, I'd like to reinstall it and experience it at its fullest settings.. this is where the frustration kicks in.
I've spent hours researching and google'ing on solutions and how to's.
In short:
-When I click update via the game client, it sends me to this site. However, it seems the only supported packages are either Trinity or Rebellion. So through a little digging, I find I need to update via Impulse.
-I go to Impulse (which is basically GameStop now) and download their application. It detects my Sins but won't allow me to update as it requires me to register. Through further research, I find out I have to go to Stardocks now..
-I login using my same credentials that I had originally signed up with years ago and am able to see my purchases of both the original Sins and the Entrenchment DLC. The serial is displayed for both.. the real kicker? It says to download the GameStop app to download and update there.
-I also download the Stardock Central app.. no luck there either. It doesn't populate any of my Sins related games.
-Within the register drop down list on the Stardock site, there is no option for Sins.. so no luck with that either.
-So to sum it up, I am told to go to GameStop, GameStop tells me to go to Stardock, Stardock tells me to go to GameStop.
.. am I missing something here? This is quite frustrating.. all I want to do is get the game updated and download/install the Entrenchment DLC so I can start playing again. Sins is an amazing game.. but this process is just frustrating.
P.S. I've emailed Stardock support days ago and have not heard back from them either..
If anyone can help, I would greatly appreciate it.
Thanks!"