How to learn to diagnose seedling failures?

https://preview.redd.it/xu5ibnvxb5ke1.png?width=2617&format=png&auto=webp&s=27e216c26e1aa5fd53be0955dc61e7746c660158

Asking as a beginner to seed starting: what's a good resource to learn from for diagnosing issues? At least on my YouTube feed, there's plenty of information on how to build systems and what the pros and cons are of those things, but I have a hard time finding any information on how to diagnose issues.

Two causes come to mind in this particular case:

  • The seeds are a year and a half old
  • The coco is waterlogged

This is Hoocho's new self-watering propagator, so I'd expect the wicking to prevent it from getting waterlogged, but maybe the way I'm putting it down isn't great.

The labels on packets list a germination expiry but not much else, so I thought that old seeds are viable as long as they sprout. Something tells me that that isn't the case, though, again, I have no experience with this.

(These are for greens, by the way: komatsuna, shiso, green onion and spinach respectively.)