You might also do a search engine query on how to fertilize a lilac. That will give you a formulation that is recommended to get the best results.
I will do just that. My neighbor’s Lilac (right next door) doesn’t bloom either. A close friend who lives two streets away... no luck on hers. I keep thinking alone your lines... it is something in the soil (especially since the one use to bloom). Something has changed... the soil test may tell me what. Thanks!