Combed larvae from cat

Hi. I am new to this site and new to knowing anything about fleas, despite being a longtime pet owner. This is my first time with fleas and I’m learning fast. Our dog has always been treated with Frontline. The two indoor cats were untreated because they never have been outside. I realize now that was not good. We discovered the fleas in mid October. We have switched the dog to Advantix and the cats have been treated twice in last 2 weeks (7 days apart) with Advantage. My house is mostly hardwood, only one area of carpet. House is vacuumed daily, steam mopped every 2 days, sprayed, animal bedding thrown away, cat tree taken outside, baseboards vacuumed, etc. In the last 3 days I have combed only a dead or mostly dead flea from each cat.  None from the dog. Today, I was combing the long haired cat. She does not let you comb her belly. I managed to get a portion of it and combed out a squirming larvae. I cannot tell you how disgusted I am. Eggs roll off the animals, right? Could an egg have stayed on her long enough to become a larvae? Or is it more likely she laid someplace there was an egg hatching? I’m so frustrated because I feel like I’m getting ahead and then this happens. Thanks for your help.