A pretreat is done just before the pouring of concrete and is designed to prevent termites from coming up penetrations of the slab of concrete. Post construction treatment is done after a home is built.
I often see termites in garages and have been intrigued as to why they occur in those circumstances rather than inside homes. I have watched homes being built and I think I see the garages being worked on last. Sometimes the concrete is poured in the home and the garage is poured last. I also seem to remember that the pretreat originally was done on the home part and wasn’t redone or even done for the garage. Now I may be wrong but I have seen that and I think this is why I see more issues within the garages rather than inside the home.