There was a rocket sled test of the Gemini ejection systems done at Edwards, I believe.
One test had the sequencing off a ..... bit.... The mannequins(crash test dummies) came plowing THROUGH the closed hatches .(,my keyboard sticks on the exclamation sign).
I'd really like to find footage of this. There has to be some out there on the Interlink.
FWIW most ejection seats are able to punch through a canopy if it doesn't jettison. There are canopy breakers mounted just above the headrests. Having worked on them in the USAF. I can tell you that an ejection is no picnic. But, it does give you a chance to survive.
Mark T