The files are sorted by the numeric year first, up to 1950.

The two files for 1950 are together, as they should be.

But the letters are sorted alphabetically, so XI comes before XV. It doesn’t see that they are numbers, it’s reading them as letters.

If they want it sorted correctly, they should rename the files:

“1950 - 018
1950 - 019”

That would work. Interestingly enough, so would:

“1950 - Eighteen
1950 - Nineteen”