After the many comments, I'll write something again, although I really only wanted to share the story.
I can understand why so many people think it's a fake story. When I first heard about this alleged arrest warrant from '94, I couldn't believe it myself. I thought it was a mix up. But I have a photo of the entry from the immigration file in front of me. I have to rely on the lawyer for the translation and of course I will not share it here.
I think BritTim's analysis is pretty close to the truth. The contacts of the lady in question deliberately chose a date of 30 years ago, so that the trail cannot be traced back to them. And of course it's impossible for me to prove that I wasn't in Thailand 30 years ago.
Suppose I would have the entry reviewed by a court. What would happen? Thais would never admit that the judiciary in the promised land of Buddha is so corrupt that an arrest warrant can simply be planted on someone after the fact. Thailand is perfect and when in doubt, it's the foreigner's fault. Besides, I just don't think it's worth bothering with anymore.
Once again it became clear to me that Thailand is unfortunately a banana republic in which you have absolutely no rights. And there are so many beautiful countries (Bali, Spain, ...) where you can live comfortably. It's certainly not perfect there either, and the countries have their own problems, but at least they're not thoroughly corrupt like Thailand.
I don't care if someone believes me or not, that's up to you. In Thailand you can live very comfortably, there are wonderful people there and I begrudge everyone if they are happy here. For me personally it's just like that, after the experiences here I prefer other countries.