I think I understand. I will be stamped 1 year ahead anytime I return prior to that "Enter Before" date. I assume that would extend to multiple entries,
I will be in Thailand in 3 weeks. If at the very end of my 1 year, I make a border run, it will be stamped 1 year later- essentially getting 2 years out of a one year visa
Unlikely. Worse case scenario, you go online and book a throw-away one-way ticket at the airport. I have never been asked to show onward travel when going to BKK. Manila is a different story.