There is no specific limit on the number of characters that can be used in the criteria section of a SUMIF()/COUNTIF() function. However, there may be other factors causing the incorrect results you are experiencing.

One possibility is that there may be leading or trailing spaces in the strings in column A or B, which can cause the criteria to not match exactly. You can try using the TRIM() function to remove any extra spaces before or after the strings.

Another possibility is that the strings in column A or B may contain special characters or formatting that is not visible, but is affecting the matching criteria. You can try copying the strings to a new column and using the CLEAN() function to remove any non-printable characters.

If neither of these solutions work, it may be helpful to provide more information about the specific results you are getting and the data in your worksheet.

1. Check for leading or trailing spaces in the strings in column A or B using the TRIM() function.
2. Copy the strings to a new column and use the CLEAN() function to remove any non-printable characters.
3. If the issue persists, provide more information about the specific results and data in your worksheet.