Thank you Catlady! An explanation! The Cestex my dogs were treated with says this ...

Epsiprantel acts directly on the tapeworm. Since it is minimally absorbed following oral administration, epsiprantel remains at the site of action within the gastrointestinal tract. Due to the digestive process, tapeworm fragments or proglottides may not be readily visible in the stool.
But it says *may* not be seen. I mostly saw them in Jake's stool, maybe he had them the worst.
As for my neighbors, they are gone, the house is empty. Her dogs did have fleas, all the time, but now that she's gone, I suppose they're looking for a home. I can't say for sure this is what happened, funny it happened after she moved out.