Korg sometimes reused number blocks for different markets, so these ranges are estimated guidelines , not absolute rules.
Here is everything you need to know about Korg M1 serial numbers. Korg M1 Serial Number
: Serial numbers typically appear as simple numeric strings. Recorded examples from user databases include numbers in the 100,000 range (e.g., 103917) and later production units reaching into the 215,000+ range [1, 5]. Famous "Pieces" of the M1 Sound Korg sometimes reused number blocks for different markets,
Unlike some modern manufacturers, Korg's 1980s serial numbering system for the M1 was relatively simple. Most M1 units feature a . so these ranges are estimated guidelines
How to verify or research an M1 serial number