Batch : label length

The example is true for MS-DOS not cmd.exe. The version of your cmd.exe is higher than MS-DOS. Feel free to use any length of label.

According to that article, this limitation is valid for :

Microsoft MS-DOS 4.01 Standard Edition
Microsoft MS-DOS 5.0 Standard Edition
Microsoft MS-DOS 5.0a
Microsoft MS-DOS 6.0 Standard Edition
Microsoft MS-DOS 6.2 Standard Edition
Microsoft MS-DOS 6.21 Standard Edition
Microsoft MS-DOS 6.22 Standard Edition

The limits are 2047 and 8192, depending on your OS. See this KB article.