In regards to another reply, there are multiple options of dealing with duplicates in calibre. From merging to deleting them.
It’s been a while since I had to do any library setup with calibre and Im kinda confused by what you are saying with “but it duplicates files when importing in a different drive where I don’t want ebooks”
Do you have multiple libraries in calibre?
Are you using multiple library managers?
Why not just use calibres folder structure?
And also if you don’t know about it - mobileread forums has been around a long time and has a whole section on calibre where you could probably get more specific help.
Dont know if it’s true or not, but I always assumed it was because the numbers get bigger left to right. Only 12 months, 30ish days, thousands of years.