I too have a QRP Labs shack clock with QLG1 GPS connected. I also fitted mine with the 20x4 display.
I found that the 16 column format was only evident during the configuration phase of setting it up. What I mean is that when you are in the menu and configuring the data and labels you want to display on each line, on first getting into the menu system only 16 columns of whatever is already stored, is displayed. If you continue to step one character at a time to the right, then the rest of the configuration line gets displayed. All the values are there - they are just not initially displayed. In fact a line of configuration can have much more than 20 characters with the 'line break' solid block character allowing you to specify different data on the line.
Once configured, when in normal operations, mine will display data across all 20 columns.
I think I am using an old version of the software - V1.01. I think the current version is 1.03c and it offers more data to display. I need to get around to upgrading mine.
73 Fred VK2WS