post an example of the long exposures that didn't come out. one thing you have to account for with film is reciprocity failure; the longer you expose it to light, the less sensitive to light the film becomes. If you were trying to do star trails and overexposed, there was probably a closer light source polluting the sky cause I think it's pretty hard to overexpose the sky at night otherwise.
although I feel like you weren't trying star trails? if you're looking at a street light or something like that, a half hour is certainly way too long. example, this was probably at like f/5.6 and 8 seconds on iso 400 film. you were at 200 so you'd have to do a stop more.