@ChikakoS , I am sorry for not being clear --- most of the forms are based on TIN ( Taxpayer Identification Number ) --- this can be SSN or ITIN. Those whom are not eligible and/or do not have SSN, you apply for and use ITIN. In your case because you already have SSN and your Tax accounts are identified using SSN, you should use SSN. That is what I was trying to get across by saying there is no conflict with your using SSN.
Also note that W8BEN essentially requires you to get an ITIN and this ITIN is valid for three years. I think SSN once issued remains valid pretty much for life
I hope this clarifies the situation
