Not a dumb question at all, Iain.
Depending on the song, you don't have to wait for the end of the verse to know the key. In fact, you can often get it within the first chord or two.
The key chord can often be recognised by those qualities I described (except the feeling of finality) wherever else it occurs.
For example - the Beatles song Hey Jude. The first chord is so strong and solid in that context that it couldn't really be anything else other than the key chord. It 'sounds' like it's the key chord, so it must be.
Apart from almost always being the last chord, the key chord is usually either the first chord, or the chord on the first strong beat (e,g., the intro to Perfect Day in A minor, which starts with E).
If it's not, then you don't usually have long to wait for it to make an appearance.
Whether it can be recognised as the key chord depends on your ear and also on how the song has been written - if it has a bunch of weird and seemingly unrelated chords - it might not be possible to know which one, if any is the key chord.
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