the last 3 years. Getting visa no problem. Only potential issue is entering Thailand but enter via a less strict border, then once your in Thailand, no problem
I got an METV from London in April. I sent 1 bank statement showing I had 5k in my account. Didn't show 6 months worth of statements. Can't comment on the employer letter as I'm self-employed and sent last years tax return and that was sufficient.