The following figure summarizes the index card method pre- and post-slide making. The red markings show how the method changes in the post-slide making period.
So now that you've made all your slides, make an index card for each slide (it was for each "idea" prior to slide creation) and write the "takeaway" message for each slide on each corresponding card. Now give a summary of your talk (to yourself if necessary) using just the index cards. I guarantee this will help you identify unnecessary slides and material that doesn't help convey the key message of the slide. You may also find that rearranging the index cards creates a smoother narrative.
So even though we started the process by creating a coherent narrative, the process of making slides erodes that coherence (it's like the childhood game of "telephone," where a secret is told and retold and comes out different after a time). Using index cards at the end will restore coherence.
There's an even broader point. You're not done when you think you're done. Every time you give a presentation you will find ways to convey the same content more coherently and concisely.