[QUOTE=Arjun31;2284686]Just checked and found that I have nearly 30 k worth old currency left from my previous visit 2014-15. I hope I can use them without any issue.[/QUOTE]Won't be a problem at all. You could use baht notes printed as far back as the 1990's without issue, earlier than that is still valid, might be worth more as a collector's item.
