Well, the back of knee pain returned, and with it pain in the biceps femoris tendon. Low level pain, somewhere between a one and a two, but pain just the same. It felt better the following day, but lingered afterwards.
I went back to the PT workouts, and it "stimulated" the injured areas, as before I was able to get to "0x0" (no pain before/after workouts). I need to continue these workouts until I get to "0x0" again, and then, rather than use just normal high-level activity to evaluate, continue until I have put four to six such "0x0" workouts together before I run again. Running puts about 2.5 times the body weight in strain on the legs, so I need to keep this in mind, increasing the intensity of the PT workouts after I reach the first "0x0" workout.
I will end on this note: The intervals on which I did run felt great. Sure, I could feel the pain in the back of the knee again, but it just felt great to be moving like that again. It motivates me to be more dedicated and thorough in getting back to the running state again.