After removing a rotted wooden frame of a basement window, I found evidence of termite damage on an attached beam. The damaged beam is honeycombed, but there is no moisture present - nor do I see insects (live or dead), wings or mud paths and the pores are not packed with dirt/fecal matter. Before I chisel out the rotted wood and build a new frame, how can I be sure that the infestation is ancient history and not a current event? Are there other signs I should look for?

Thanks for all advice!