I assure you it is a standard practice, but why would recruiters discard resumes without exact dates 'by default'? Because the assumption is that those people a

I assure you it is a standard practice, but why would recruiters discard resumes without exact dates 'by default'? Because the assumption is that those people are 'old'? That may answer the question for you, but ageism is a legal concern and disqualifying candidates because they didn't tell you when they graduated isn't dissimilar to asking someone how old they are in a job interview and refusing to hire them if they don't.