I also had the same problem, illegible/very hard to read BC from NSO what i did was post about it on their guestbook page:
http://www.census.gov.ph/data/guestbook/index.htmlafter a few days or a week, I received an email from their Civil Registration Department head, Ms. Lourdes Hufana, she told me that they will request another copy of my BC from the local civil registrar coz the copy they have was blurred out by age. I have yet to find out if my NSO BC will be clearer now coz i have not gone back to NSO yet, will do so next week.
I have read here of someone who had a blurry NSO BC and who did not have problem during interview. Just bring the copy from the local civil registrar together with the blurry NSO BC. And don't worry too much coz they will verify here birth certificate with NSO anyway (doc. verification).
Good luck to you and to your fiancee. God bless you always.