virtualbox.org

For some reason my clients VM crashed on them and they tried to fix it themselves. During their research they came across the merge feature and tried it. It seemed to have copied over their existing data with a older VM that was saved on their computer. Is there any way to get the 2018 data back?

You don't give too many details, but it sounds that they merged (removed) a snapshot, and that snapshot was removed. The only way to get back to where you were is to restore from a backup.