Peter, if you sent a CMYK file saved with the euro color space and the printer was not using this the shades of colors you expected to see when printed would be not be exactly the same. At this time euro is outdated and there are different swop (Specifications for Web Offset Publications) and jcolor standards even for what type of stock the images are printed on. If you look at color settings in Photoshop you can get an idea of how many different standards there are.