Please do not call it a requirement. That is totally incorrect. It is at best a yardstick to gauge risk of being accused of misrepresentation by USCIS and this yardstick exists only amongst applicants and their hired lawyers. There is no regulation as far as USCIS is concerned.
I know requirement is a bad choice of word. I first used rule and felt requirement is a little soft word than rule
It is neither a rule nor a mandatory requirement but a good to follow specification by immigration experts to avoid unnecessary pain during AOS.
Geez, I am still looking for a better word.