When the Valiant first flew they worked out that the ejection seat in it was not powerful enough to get the pilot over the tail. They designed a bigger seat and they were in the hangar awaiting fitment when they had their first ejection; with fatal results when the a pilot hit the tailplane.
The canopy/seat syncrynistion was a tape between the canopy and the seat firing blind. Until canopy the departed one could not pull the handle. In the sixties they added a seat pan handle that was called the alternative firing handle. With this one you could fire the seat with the canopy on. Should you do so the Pilot's Notes advised you that the results would be fatal.
There was a pin for this between your legs and the sensible people I flew with were quite happy fo it to remain there. Some times you would have a keen captain: Two inches between his Flt Lt rings, rugby ball and bible in his nav bag who would insist on them being removed. I would come back after one of those trips with no fingertips on my gloves. Luckily very shortly after that they scrapped them and I transferred to and then had a glorious life flying helicopters all over the World.