"could" being the past tense of "can".

"could" is often stated as being the past tense of "can". That is definitely not the case, rather the past tense of "can" is "was able to":

"I can go there" (present tense)

"I was able to go there" (past tense)

"I could go there" means something entirely different from "I was able to go there". "could" is not the past tense of "can".

"I'll go see if I can" (present tense)

"I went to see if I could" (past tense)

Okay, in some contexts "could" is the past tense of "can" but certainly not in all contexts.

I think "could" is the past tense of "can" in all contexts. Why not? Can you think of any specific examples?

Could is the past tense of can but it's also a conditional tense marker, so I guess it can be ambiguous in certain circumstances. Like the example you gave.

"I could go there"

Can mean either, "I was able to go there and now I can't" or "I could go there if...blah blah".

<<"I could go there" means something entirely different from "I was able to go there". "could" is not the past tense of "can". >>

"I could go there" can mean both "I was able to go there" AND "I might go there"/"I might be able to go there" depending on how you stress it. Could is still the past of can.

You could also say "I could have gone there" to mean "I was able to go there"

"Could" is the morphological past tense of "can", and it's used that way in various situations:

"Could he see it?"
"Could she hear him?"

But I've noted in the past that the compound verb "to be able to" does fill in a lot of gaps in the paradigm of "can". For example, the practical infinitive form of "can" is "to be able to", and the practical future tense is "will be able to". And I think you're right in pointing out that in some instances, the past equivalent of "can" would be "was able to".

This is an example of where German is much simpler and without the ambiguity of English

Ich kann das machen - I can do that

Ich konnte das machen - I was able to/could do that i.e always past tense of 'can'

Ich könnte das machen - I could/might be able do that) i.e. to express the possibility in the future

"I could go there"

Can mean either, "I was able to go there and now I can't" or "I could go there if...blah blah".

There's also I COULD HAVE GONE THERE.

It seems 'could' can only be used as the past tense of 'can' when there is some other information in the sentence which makes it clear that the past is being referred to.

"I could have gone there" doesn't really have the same meaning as "I was able to go there".

<<"I could have gone there" doesn't really have the same meaning as "I was able to go there". >>

"I could have gone there" includes "I was able to go there", but not mutually.

"I was able..." is more restricted in meaning

Assumption:

She could have been there (yesterday). = She could be there (yesterday) = Maybe she was there (yesterday).

The sentence: *"She could be there yesterday" is not possible for me. The word "could" in "I could", "you could" etc. has more to do with the future than the past. After a pronoun/noun, the past tense of "can" is "was able to", with "could" when occurring after a pronoun/noun meaning something entirely different.

<<The sentence: *"She could be there yesterday" is not possible for me. The word "could" in "I could", "you could" etc. has more to do with the future than the past. After a pronoun/noun, the past tense of "can" is "was able to", with "could" when occurring after a pronoun/noun meaning something entirely different. >>

'could' works both ways

as an indicative preterite ("She could be there yesterday/She could have been there yesterday")

OR

as a subjunctive preterite ("I could be there tomorrow/I could be someday/it could be true")

In modern English, the forms have merged for both, where, as someone pointed out earlier, German reduces the ambiguity by preserving distinct forms for each