I recently stumbled upon this wikipedia page and it got me thinking. Take a look at the following table (terms are lifted from the Wikipedia page)
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?