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Where, here, and there: What is the origin, and can it be generalized?

I recently stumbled upon [this wikipedia page](https://en.wikipedia.org/wiki/Pro-form) and it got me thinking. Take a look at the following table (terms are lifted from the Wikipedia page)

| W (interrogative) | H (proximal) | T (medial) |
|-------------------|--------------|------------|
| what              | ?            | that       |
| when              | ?            | then       |
| whence            | hence        | thence     |
| whither           | hither       | thither    |
| where             | here         | there      |

These are the ones that I could find an obvious correspondence for, but I'm curious about the general pattern, especially since there are a number of outliers ("who" has no corresponding H- or T-word, for example, and "these" has no W- or H- word).

Was this a general form at some point, and English simply lost some of the entries that would be in this table, or were these the only cases where the W-H-T forms have ever existed? If the former, what were those lost forms? If the latter, why?