You're definitely remembering correctly. I can't speak as clearly to Buck Rogers, but the pilot episodes of BSG (collectively entitled "Saga of a Star World") were edited together for a limited theatrical release. I remember seeing the movie in the little theater next to George Mason University in Northern Virginia - it was the only place I could find showing it back then, to my recollection. It had several different scene versions, including the part where the Imperious Leader has Baltar beheaded, as opposed to staying the Centurion's blade in the series, after which they introduced Lucifer as his new handler. IIRC, that was the only showing of episodes in a theater.
Several other notable re-edit telemovies were made, such as "Living Legend", assembled from both Pegasus/Cain episodes of the same name, "Mission: Galactica, The Cylon Attack", also taking bits from "Living Legend" and "Fire in Space" scenes and "Experiment in Terra", which is a HUGE tapestry of pieced together parts of "Saga of a Star World", "The Magnificent Warriors", "Fire in Space", "Experiment in Terra", and Galactica 1980's "The Super Scouts, Part I" and "The Return of Starbuck". The beginning act also has scenes spliced from "The Living Legend, Part I", in terms of closeups of the Pegasus. It also had a new scene of Earth Astronauts finding the Galactica's logbook floating in space, showing new footage of original reptilian Cylons:
The Battlestar Wiki has a list of all of them, including all the episodes that were used to build them. There were quite a few.
Glen Larson must have loved doing those things and so did Universal. Very little effort to make something ostensibly new. Much like an Eaglemoss model repaint.

It would stand to reason that they did it for Buck Rogers as well.