@Ant****
The “free extension” is an automatic visa extension, meaning you don’t get a stamp in your passport. The first one that required you to get a letter from you embassy was not automatic.
Even today, if you go to immigration you can pay 1900 baht for an extension. You don’t need one, but you can pay for one if you want. Chiang mai immigration has a waiver on the top of their applications stating you know it’s free but still wish to pay 1900 for an extension.