Thank you for your interest in SDL TMS and your suggestion for a new idea to improve the product. It's quite possible to upload a file with fewer segments that the original in case the translator has joined segments together. At present, we have no real way to validate the upload of the SDL XLIFF file but I'm sure it's something that could be improved in the future. I'll leave this under community review for now and see if any other suggestions arise. In the meantime, I suggest that you prevent your users from using third party applications that may corrupt the SDL XLIFF file.