如果Mac错过了OS升级，或还原后版本太低，无法更新或升级到后续版本。在App Store是只能搜索到最新版本的(是无法搜索到除最新版的其它版本OS)，版本太旧是无法通过App Store进行更新的，不更新就用不了最新的App，SO，你正在找的2个旧版本OS链接已为你准备好，请惠存。
App Store link(10.12: "Sierra" (June 13, )):Get macOS Sierra
App Store link(10.13: "High Sierra" (June 5, ) 4.80GB ):Get macOS High Sierra
Mac OS各版本号、代号、发行时间表：
Public Beta: "Kodiak" (September 13, 2000)
Version 10.0: "Cheetah" (March 24, 2001)
Version 10.1: "Puma" (September 25, 2001)
Version 10.2: "Jaguar" (August 23, 2002)
Version 10.3: "Panther" (October 24, )
Version 10.4: "Tiger" (April 29, )
Version 10.5: "Leopard" (October 26, )
Version 10.6: "Snow Leopard" (August 28, )
Version 10.7: "Lion" (July 20, )
