I never remember doing that. I was on a Business visa for three years and then changed to a Non-B extension based on marriage. The only forms I remember having were the K.2 and K.3. And I did the first extension in Korat, so we were nowhere near Lamphun where our marriage was registered. Well, best of luck. Maybe you give it a try without the 6.1.3. What's the worst that can happen - they insist you show it. If they don't insist, you're good to go. And realistically, how difficult is it to get another original of the certification letter. Interesting though, I can see certifying you've been divorces, but how do you certify that you're single? That's pretty much your word. It's not like countries provide their citizens with certificates of singleness - not that I've ever experienced?