Hello, first I do not print any boxes, but usually the programs respect the files sizes, if you are download from here, I suppose that the measures are good, then try to check when you print, that your printer software do not have "fit option" checked. There will be a option for real document measures or even a preview for print document. I use photoshop and it have it. You can see the page and a preview. For exact measures, sometimes it changes for different printers, and it is a "try and error", putting sometimes a few mm more.
For measures, it depends of the box that you want to print, I only know the snes or sfc boxes measures, you can open in any photo software and check about they, Gimp is free software, but I do not know about it. Usually, there are an option for image-->size where you can check the file size.
If the measures of the box are good and your printer is not changing anything, it will be printed good. Adobe acrobat too respect the original sizes, but if you choose the correct options. I do not know what software you use, what printer and if the problem is a few mm or half size.
Every software and printer is different, check correctly all the options.
I hope that it helps a little.
Regards.