Apple - Old versions of the OS X Human Interface Guidelines

It wasn't easy, but I think I got all of them.

2006-10-03:

https://web.archive.org/web/20070520203932/http://developer.apple.com/documentation/UserExperience/Conceptual/OSXHIGuidelines/OSXHIGuidelines.pdf

2008-01-15:

https://web.archive.org/web/20080225084449/http://developer.apple.com/documentation/UserExperience/Conceptual/OSXHIGuidelines/OSXHIGuidelines.pdf

2008-06-09:

https://web.archive.org/web/20081222045913/http://developer.apple.com/documentation/UserExperience/Conceptual/AppleHIGuidelines/OSXHIGuidelines.pdf

2009-08-20:

https://web.archive.org/web/20110604173215/http://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/AppleHIGuidelines/OSXHIGuidelines.pdf

2012-07-23:

https://web.archive.org/web/20121004065110/https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/AppleHIGuidelines/OSXHIGuidelines.pdf

2013-10-22:

https://web.archive.org/web/20140603021344/https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/AppleHIGuidelines/OSXHIGuidelines.pdf

Introduction (HTML):

Saved 49 times between August 5, 2011 and June 14, 2016.

– and at the time of writing, the earliest capture presents a page with a suggestion of 1,613 captures over a more extensive period, beginning 2010-09-09.

The PDF versions linked from the accepted answer provide a more useful way of comparing versions of the Guidelines at points in time.

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Side note: from http://forums.macrumors.com/threads/1979059/ it seems that for a while, captures such as http://web.archive.org/web/20140815012123/https://developer.apple.com/library/mac/documentation/userexperience/conceptual/applehiguidelines/Windows/Windows.html#//apple_ref/doc/uid/20000961-SW13 (OS X Human Interface Guidelines: UI Element Guidelines: Windows) were not available from the Wayback Machine.