I know bug MC-4597 talks about Fireworks not being in the Creative Inventory because there are literally millions of possible ones, but with the introduction of the "Flight Duration 1, 2 and 3 Fireworks Rockets," I think this could now be considered a new bug on a new item...though it was not a bug with the OTHER fireworks rockets before... (I was trying to get them in a mini-game and had to give myself the individual crafting items and make them. Not the end of the world, but thought I'd mention it anyway!) Cheers!