According to dictionaries I have consulted, "that's" is contraction of "that is" or "that has."

Can "that's" be used as a contraction of "that was"?

That is what we thought.

That is what we had planned.
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But for some reason I hear people say that's what we thought or that's what we had planned but it didn't go through. Those are sentences I've heard native speakers use on more than one occasional!

Please explain!
 khoff's reply was promoted to an answer.
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Shouldn't it be that was what we thought?

That was what we had planned but it didn't go through?

Since it's all in past tense?
This has already been answered in another thread.

Please don't keep asking the same questions in different threads.