Can I enter Thailand as a tourist without proof of a ticket for a departure ?

Thank you

Hi all, would love some advice / guidance. I have an Irish passport and was in Thailand for just under 4 months (April - July 2019) on 30 day tourist visas (successfully got extensions on tourist visa). I then came home to Ireland and applied for a 6 month Multi entry tourist visa which I was granted and is effective Aug 2019 - February 2020. I had planned my trip for 15th September to go over until February. However due to an illness in my family I may need to postpone my trip until possibly next year. What would I need to do in terms of the active visa and reapplying for a time to travel next year? Or if I decided to go in for example January 2020 would I only have 1 month valid on the visa and need to leave February? I appreciaite any advice. Thanks