Columns First
Masayuki Akimoto used a corners then middle layer edges method in 1980.
A June 2002 example of the idea.
Technically this may be classified as a Belt method variant. But it reaches the columns state so the classification is blurred.
A May 2004 example of the idea that starts with four pairs.
A November 2007 example.
Kenneth Gustavsson posts the idea, also in November 2007.
This is what became PCMS.
Kenneth's website for PCMS.
Michael Gottlieb adds a variant of PCMS to his site.
The post from the screenshot above states that multiple methods were added to the site. The PCMS variant was likely added at the same time as evidenced by there being no mention of the link to the Columns First page prior to March 20, 2011.