I guess in the sense that there was some notice of the impact on bone marrow during World War I but it wasn't until the work of Gilman et al during the Second World War that there was progress.

Not really. The link wasn't made until World War II, though nitrogen and sulfur mustard were first used as weapons during the First World War.

The first chemotherapy drugs, some of which are still in use, are alkylating agents, and they're basically chemically similar and derived from mustard gas (which isn't a gas, incidentally).

No, however, every time a reserve is packed it marked with the number of packs and whether it was a repack (marked with a / mark) or a deployment (or more commonly a "ride", marked with an X). A reserve parachute normally has a lifespan of 20 years or 40 repacks, after which it can be sent back to the manufacturer in some cases to be given a more detailed inspection to see if it's still airworthy which it likely is. In some countries (mostly in Europe) riggers won't pack a reserve older than twenty years, but some people in the USA will buy them cheap there and get them inspected and keep using them if airworthy.

Reserves are generally inspected and repacked every 180 days although there really isn't actually a need to do it more than once a year according to people who are far more expert than I am, however, rules usually require that 180 day repack.

Anytime you go to a new DZ you can expect to have to show the packing card and the rigger's seal on the reserve to be able to jump. At events or big DZs they'll often put one of those plastic wristbands you get at concerts and resorts in the harness main lift web so the rampers can quickly verify them as you get on the plane. The most commonly used DZ management software also can record repacks and won't let someone manifest (get on the plane) unless they're current.

Most DZs have a rigger on site who can perform the service. They normally work in what's called the Loft, which I'm told comes from the fact that they usually worked in the loft section of hangars.

Exactly. 50% safer than flying!

The thing with that video is that guy knows little or nothing about sport skydiving. He thinks things are careless because of the very very systematized way he was taught, which isn't how it works in the sport itself.

I don't know about your grandfather but I've never seen a perfectly good airplane myself. And when it comes to plane crash fatalities they usually involve hitting the ground so I'm good with not being around for that part!

Extremely. Parachutes do malfunction sometimes, but the common malfunctions can be quickly remedied by Emergency Procedures all skydivers are taught thoroughly. If they can't, then the main can be "cut away", which is actually not cutting but the deliberate release of the parachute from the harness, followed by the deployment of a reserve parachute.

While most skydivers pack their own main parachutes, reserve parachutes are packed by specially trained and licensed parachute riggers and the process of packing them is much more detailed and thorough. They're also designed to deploy quickly and reliably.

Most skydiving fatalities have nothing to do with parachutes malfunctioning though. Much more commonly it is a poor decision made by the skydiver like a low turn while trying to execute a high performance landing that is the culprit. Occasionally it's a medical incident during the skydive. The odds of a double/total malfunction are astronomical.