Does Wisconsin have duplicate voter registration numbers?

No. All Wisconsin voter registration numbers are unique.

Wisconsin voter registration numbers consist of at least 9 characters and are alpha-numeric. This means they may include both numbers and letters.  They may also begin with any character, including a zero. Thus, the registration number is really a special code and not merely a number.

This small distinction sometimes causes confusion because people (and some common programs) often ignore leading zeros. For example, Microsoft Excel will automatically remove leading zeros from entries it identifies as numbers. If someone opens a CSV (Comma Separated Value) file in Excel without preserving leading zeros, Excel will erase them all. Thus, 000012345 becomes 12345. To preserve the digits, a user must access the original CSV file and import it to Excel using the “Get Data” tool. Or use dedicated database software such as Access to open the file. 

It’s worth remembering that computers don’t "read" numbers like we do. A computer considers each individual character equally. To the computer, the character zero is just like any other and its meaning must be defined. You have to tell a computer to ignore a leading zero (as Excel does). 

Finally, the use of alpha-numeric codes including zeros makes Wisconsin voter registration ‘numbers’ significantly more complex than a mere number.

Characters                 Number of Possibilities Alpha-Numeric          Number of Possibilities Numeric Only (1-9)

1                                 95                                                                                   9

2                                 4,465                                                                              99

3                                 138,415                                                                          999

4                                 3,183,545,000,000                                                         9,999

...                                                ...                                                                       ...

10                               10,104,934,110,000,000,000,000                                  9,999,999,999