Hi Daffies,
Welcome to the Garden Web. If you haven't potted them in a year I would venture to say that it could be the problem. I repot standards every 9 months to a year. I repot minis and semis every 3 or 4 months. If and when you do repot just make sure that your mix is very light.
If you email me I can send you three pages of what I have passed out to people when I went out to speak. My email is FredCHill@comcast.net
Fred in NJ

Welcome Daffies!
I am fairly new to the care of African Violets as well, but Fred gives excellent advice.
Have a wonderful day,
Raven

I'm also fairly new to the AV's but having so much fun with them! Welcome Daffies to the forum!
Possibly re-pot your non bloomers and they will start some budding soon. Standards should be re-potted every 9 months and the mini/semi every 3-4 months.
Also a cocktail of fertilizer diluted with each watering will help also in that dept.,,,Debbie

I highly recommend putting the pages Mr. Hill sends you into document protectors and keeping them handy. I refer to them often. Welcome and Good Luck!