I can assure you that data does not disappear suddenly & mysteriously.

If you are confident that neither you nor anyone else in your office has cleared History, then the only other possibility is damaged data.

When you say that Softrak helped you, did they do a Data Repair? Has anyone else done a Data Repair? If you check Data Integrity now, is it error-free?

If you want a safety net, run the Backup procedure on the File menu on a weekly basis. That gives you a set of data to go back to if necessary.