Not for the small quantities involved in the classic British items. Its not like the modern stuff, there are limits 5kg in powder content but I'm no where near those , fireworks are powder mixtures to give the various effects and not gunpowder in the sense of cannons etc. Bangers have small amounts of blackpowder but it would take a lot . Imagine how much people have around bonfire night if they buy only a small number of the big display cakes that are the norm. Fireworks degrade in efficiency with time and unlike explosives become less volatile. Sometimes we find common old items but with badly stored/damaged labels and people will fire them to see what they are like, in many cases they will burn but don't perform as well as they did back in the day. A lot of collectors own firework businesses doing some of the biggest displays in this country and around the world so there is a wealth of knowledge within the vintage firework collectors fraternity.
It's all about preserving the little that is left of a once thriving British Industry, now all gone. Many items turn up as shop dummies, each company supplied a range of their fireworks without filling that were purely for shop display, like for example these 1937 Standard Display Boards. An idea that was carried on well into the 60's and early 70's. Then once small single firework sales were banned in 1976 and items had to be bought in selection boxes they made boxes with dummy items like these Brocks boxes from the early 1980's.