Check numbers that are preprinted on check stock may be suppressed in PrintBoss.
In PrintBoss, navigate to File / Open Document Work files. Select the correct file name for the type of check, and choose Browse.
Double-click on the last record in the grid to display the check template. Select the check number to turn it blue, then right-click and select Comment Current Object. The check numbers are then suppressed when printing checks.
Repeat this process for each template type being used.