Previously, the fact that the basic recipe for fireworks (paper and gunpowder) doesn't show up in the recipe book has been marked as a duplicate of MC-115229 and closed as 'works as intended'. This makes sense for complicated recipes like banner patterns and fireworks using firework stars, as you can use pretty much whatever combination you want and the recipe book can't really provide an exhaustive list.

However, it doesn't make sense for the basic firework recipe without firework stars. Since they are used to propel you when using elytra it's a commonly used recipe and it would make sense to include it in the recipe book.