@Christopher **********
No, you're confused. The T.8 form asks you to upload your yellow fever certificate in electronic form. You will be REFUSED boarding if you are beginning your journey from a yellow fever region. This new rule was strengthened in August of last year.
No ifs or buts about it. It was all over the news.
So to fly to Thailand from one of those 45 countries, proof of yellow fever vaccination is MANDATORY.
There may be ways of getting around it; by flying on separate tickets via Vietnam or Europe or something, but if you insist on flying direct (with a transit in somewhere like Dubai) proof is needed. In fact, it may be required just to get to Dubai!