I don't know whether the activity already happened or not when a sentence contains would. 

I've found a couple of examples about this would in a textbook that I have, and so I'll quote them to make my point clear. 

a) They left the house at 6.00 a.m. and would reach Edinburgh some 12 hours later. (=they reached Edinburgh) and

b) He was sure that the medical tests would show that he was healthy. (= we don't know whether he was healthy or not)

Where is the line between a) and b) ? What makes them different kinds? Why can't we tell if he was health or not, while we can tell they reached Edinburgh?

Thank you.
This is type (a). He's telling a story, and he knows what the ending is going to be. In this style, "would" is positive. definite.

If he wanted to convey the idea that while they were waiting there, they were uncertain as to whether anyone would show, he'd say, "waiting for blind people who might never show."

Type (b)?? "My friend told me he was sure the blind people would [not] show up."

BTW, "I imagined how the hand might look." "I imagined what the hand might look like."
Aha! You do know the answer!

a) is a narrative style. The author is understood to be relating a series of events which have already occurred (perhaps fictiously) and the outcome is known.

b) is a statement that someone has expressed a personal opinion. The tests may or may not have even occurred.
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Thank you for the quick reply, but I'm still being confused.

Let me please post one more example I've found in Who's the Chef written by David Sedaris.

While sitting there, just the two of us, waiting for blind people who never showed, I imagined how the hand might look like. 

OK, it's clear that no one showed up, but what if this sentence went like, 

While sitting there, just the two of us, waiting for blind people who would never show, I imagined how the hand might look like.

Can we still tell whether or not someone showed up?

Will you make clear examples for a) and b)?

Thank you again. 
 Avangi's reply was promoted to an answer.
Thank you for the quick replay always and now AHA! I understand it!
Key phrase was personal opinion for b). 

And, also thank you for your BTW help.

It's not easy to realize my mistakes on my own, so. 

I appreciate you.
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