Wear causes looseness. I don't get to hung up on a chain stretching, as long as it only has a bit of pull off the rear sprocket, a few mm or so.
It's the wear itself you should be looking at. If the chain is flapping like a wizards sleeve it can hop off the sprocket but I don't think yours is that flappy.
You need to check for tight (seized) links, broken seals, oval pins etc. Damage. Your chain coming to a sudden stop at warp speed is a real eye opener. And wallet opener for that matter. Other things open suddenly, too.
What are your sprockets like?
So yeah, don't get hung up on a load of measurements, check the condition, link by link.
My 2c anyhoo.
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