Scientific papers many times have citations of the kind "private communication." APA has a style guideline so certainly not looked down on: https://apastyle.apa

Scientific papers many times have citations of the kind "private communication." APA has a style guideline so certainly not looked down on: https://apastyle.apa.org/style-grammar-guidelines/citations/personal-communications https://apastyle.apa.org/style-grammar-guidelines/citations/...