A colonies production of infrastructure does not seem to be added to the producing colony. I believe this applies to both types, as I have never seen a multiple other than 5 for regular infrastructure except when imperial freighters pick up non 5x amounts.
Additionally, LG infrastructure does not seem to be traded either as far as I can tell. I have seen regular infrastructure traded, along with wine, and plastics, but running several years with 10 LG colonies, some full of people and infrastructure, and some demanding, has not changes the total amount of LG infrastructure by even 1.