Header numbers

There are pages named "Translating:Group statistics/Header*", where * is a number: Header1, Header 7, Header10, etc.

What are they for?

It looks like most of them are not linked from anywhere. Are they just old experimental versions of Header10? If they aren't used, can they perhaps be deleted?

Tagging people who were involved in editing them: User:Hamilton Abreu, User:Jon Harald Søby, User:Siebrand, User:Robby, User:Shirayuki, User:SPQRobin, User:Nike.

They are part of templates used on archvied statistic pages; some of these pages were translated, some were edited multiple times and their headers changed and retranslated. These may be old headers that are no longer in use, but some of them are still in use (Header7 and Header10; but may be not for the same sets of languages). Historically these pages were not created usnig the translate UI interface, which started being used much later. These headers seem to have changed over time when the contents generated by a bot were archived and kept. Snice long now, these reports are no longer archiving pages, so only the last header version is useful. The number of columns computed in the report changed over time, and initially these were not always refreshed by a bot but manually. If ever there's a new change in the number or contents of the columns, a new header would be needed for the next run of the report, while the existing one would remain as long as the new report has not been updated. This many explain why older headers were left behind: you can see all these headers used in the historic versions of the statistics page.