But what about after they leak? Wouldn't the hydrogen then mix with air and get below 74%?

If this is set up similar to other LTA airships (simplified, its bags of air contained by the outer skin with a structure supported by a very light airframe), then a wayward bullet might pierce one or two of these cells - which a certain number of these are allowed to deflate before problems begin. Also, most shot-sign mischief is carried out by shotgun and the max vertical distance it can travel is considerably less than 1000ft.

thank you for the insight, that's very interesting

Fuel, Oxygen, Spark.

You need all three.

It is more complicated. You also need fuel/oxygen ratios that allow for sustained burning, else any fire extinguishes quickly. And heat. There are many fuels that just don't burn unless you heat them up and control their burning to heat the incoming fuel.

Yeah, I wasn't thinking full Hindenberg, just damage would be expensive enough…

Shooting the thing and watching it come down might be fun enough for some.