Squashing

Can you help us clarify the legal/IP requirements towards squashing?

When using GitHub one of the options to get a branch into the mainline is to perform a pull request and then "Squash" the pull request into the mainline. This is the git equivalent of git squash and git rebase and adding all authors as Co-authored-by.

Which seems to match the Handbook perfectly:

An Also-by (or Co-authored-by) entry can be added for each additional author of a commit (one committer per entry). This might apply, for example, if a commit has been authored via pair-programming, or the commit is the result of collapsing multiple commits authored by multiple developers.

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The provided NOTICE file states:

All content is the property of the respective authors or their employers. For more information regarding authorship of content, please consult the listed source code repository logs.

But how would someone know whom the content belongs to, if commits where squashed and we now have a single commit with multiple authors?

The only record is in the pull request itself on github.com, which is not persistent (assuming we don't trust availability) and not directly in the "source code repository logs".

Do we need to disallow squashes with multiple authors? We are confused. The idea is to preserve individual copyright for the authors.