1966年在中发［66］277号《中共中央文件》中说，杨尚昆同志“不顾中央多次关于禁止安设窃听器的决定，背着中央，私设窃听器，私录毛主席和中央常委同志讲话，盗窃党的机密”。
http://www.mps.gov.cn/n2254860/n2254883/n2254885/c3697011/content.html
1966年2月，中共中央、国务院中发（66）第119号文批准，建立开阳特区, ...
This is from .gov.cn. http://www.kygov.gov.cn/zjky/xzqh/201609/t20160914_1010150.html
These are from Chinese government. Try "中发（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 档案出版社,
中发( 66 ) 301 号 ...
From less "credible' sites, you can see 中发（66）第268号 was issued in May 1966 too.
