Do you posit that there are enough examples of 30x8 ellipses encoded in braille online for ChatGPT to learn from but not 31x7 or 31x9 ellipses? That seems unlikely.
Yes, or the model got lucky with the quality of output for a particular combination of my prompt and the reasoning behind its answer that lined up with something it had seen before — quality which it was unable to recreate under slightly different circumstances.