Is it possible for an attribute table to display more than 255 columns?

Yes, it is possible for an attribute table to display more than 255 columns. By default, the maximum number of columns in an attribute table in ArcMap is 255.

A problem arises when importing an Excel table (.xslx) with more than the maximum number of columns, the number of columns in the imported table is truncated to 255. In some instances, when joining an Excel table containing more than 255 columns to a shapefile, only 255 columns are present in the joined table.

To import an Excel table with more than 255 columns, save the Excel table as a .csv file. Add the CSV file to ArcMap, and all columns are displayed.

Note:
ArcGIS supports Excel 2003 and earlier .xls files, as well as Excel 2007 .xlsx files. Excel 2007 allows much larger worksheets (1,048,576 rows by 16,384 columns) than in Excel 2003 (65,536 rows by 256 columns).