The name refers to the fact that even a simple concept like "which model generated this image" has completely different representations across tools. ComfyUI records a file path to a checkpoint in a JSON workflow graph. Midjourney records a version flag (--v 6.1) in a text string. DALL-E records a model name in an API response. Same semantic meaning, entirely different structural representation.
The two metadata problem is not just about formats — it extends to metadata richness. ComfyUI provides over 100 fields per generation. Midjourney provides 5-10. DALL-E provides 3-5. A normalization pipeline must accommodate this asymmetry without losing the rich information from detailed sources or failing on sparse sources.