How to disclose past TN denial during AOS
My first TN at Niagara Falls land border back in 2011/2012 was denied couple of times because the application was weak (i.e. missing critical information in the support letter). I was allowed to enter but not on TN status. On third attempt I got approved. I held multiple TN visas after that without denial.
During AOS application, I disclose this as denial of visa or denial of status and do not need the details as I do not remember as it was 14 years ago.