1966年在中發［66］277號《中共中央文件》中說，楊尚昆同誌“不顧中央多次關於禁止安設竊聽器的決定，背著中央，私設竊聽器，私錄毛主席和中央常委同誌講話，盜竊黨的機密”。
http://www.mps.gov.cn/n2254860/n2254883/n2254885/c3697011/content.html
1966年2月，中共中央、國務院中發（66）第119號文批準，建立開陽特區, ...
This is from .gov.cn. http://www.kygov.gov.cn/zjky/xzqh/201609/t20160914_1010150.html
These are from Chinese government. Try "中發（66）site:gov.cn" in google and baidu yourself.
Below is not directly from a Chinese government source. It is on google site and claim from 檔案出版社,
中發( 66 ) 301 號 ...
From less "credible' sites, you can see 中發（66）第268號 was issued in May 1966 too.
