回複：Don't waste your time on overseas letters!!!

Dear friend
I DO NOT agree with the previous replies. I was NIWed by lawyer. He didn't tell me to get letters from overseas. Furthermore, from my experience and knowledge overseas experts are not in a good position to judge if your work and contribution is in the US interest. International recognition is critical for EB1b, but carries little weight for NIW. On the contrary, based on the requirements for NIW it is critical to prove that your contribution is far better than a minimum qualified US citizen. You don't have the burden to prove you are better than international peers.
The key points:
1. National (meant US) interest: "National' here does not only mean this country, it also means the benefit of your work should be National in scope, not regional. Many applicant overlooked this.
2. Your work is far better than a minimum qualifed national (refers to US citizen). This is the foundation to waive the requirement for PERM.

Strongly suggest you put all your efforts to look for domestic references. Preferably those from goverment or serve as counsels for goverments.
Good luck!