通过/经过 as prepositions - Differences?

I'm looking at 通过/经过 in both an old textbook of mine and on the Chinese grammar wiki right now. I think I mostly understand how to use them as verbs, but examples like this are confusing me.

1) 经过自己的努力，她考上了北京大学

2) 通过这个调查，我们发现很多人都支持他

3) 通过他的介绍，我认识了我现在的老板

In terms of structure, Chinese grammar wiki says...

经过 + Event / Time ，⋯⋯

通过 + Agent / Method ，Subj. ⋯⋯

Which sounds simple enough until I look at the examples. In example 1), why is "自己的努力" considered an "event", rather than a "method"? Can I not use 通过 in examples like example 1)?

Also, in example 3), I get why "他的介绍" is considered an "agent/method", but could it not also be considered to be an event too. I mean, the introduction was a situation that took place, right?

I'm a bit confused right now.

submitted by /u/BillyBattsShinebox
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