thanks so much for this info, gonna go to Taipei to get this visa too. For the EIN, what document did you provide to prove this? Was it the original issuance letter from IRS (CP-575) or something else?
I recently got a new passport in Bangkok. When I left Thailand going to Malaysia I gave Immigration my old passport with the corner cut off, they stamped it, didn't ask anything, didn't refuse it, didn't ask for my new passport. So it can be used for travel and international travel. Not sure I would rely on this one incident as proof its possible though! :)