We receive tax forms based on employment from May to Dec. I've only received forms from 2 schools for December to end of contract. Im sure they report. Am I missing out of any serious refund money say for 3 mos. or best I just let sleeping dogs lie? Possible they'll just give me earnings statement tell me the sort it. Going on holiday, thank you in advance.

You could have paid too much tax, have a look here:

 

http://www.rd.go.th/publish/6045.0.html

If I were you, I'd file anyway.. As noted, you may have overpaid and eligible for a refund.  As an aside, I tend to get a small refund each year and I've always received my refund (via paper cheque) in fairly short order.. The other upside to filing is that I recall is that MoL (Labour) now requires proof of tax compliance for renewal of a WP..  So, filing might also help you IF you have a WP or will renew a WP.