Then its possible the damage was done prior to the perimeter treatment.
Terminex can only spot check the exposed interior. I do not think they or anyone else will guarantee what they cannot see. The only tell tale signs of termites are the mud trails they leave under your exposed floors and along joists and base plates. Read your guarantee or warranty to see exactly what it says.
In future treatments, follow the inspector and if he spots these mud trails, have him make a note of it and give you a copy. When you decide to have the treatment done, tell the technician you want him to clean up all the mud trails and make note of their location on his job report and get a copy of that too. Then from now on, you will have proof that any future mud trails will not be mistaken for old trails prior to the treatment and they won't be able to claim otherwise and you can get a free treatment.
Also if you do get new mud trails too soon after treatment, then I suspect the company did not dilute the chemical properly or did not apply enough or spaced each spot too far apart. Then it may be time to look for another dealer. I believe each spot should be between 1-1/2 to 2 feet apart. Good luck.