I would say it is wuite possible. There are a lot of differneces, and I am sure our local SQL experts will comment on those, but form the basics,
Navision Backup and restore does a lot of checeking a long the way. And in particular secondary keys are re-built during a restore.
In SQL for example, you could have invalid Navision data in a field that is part of a secondary key, inthe SQL restore that invalid data is brought across, but through Navision it is corrected. Also you could have had a bad netwrok connection, or a bad disk sector that allowed bad data to be written to the database. Again the Navision backup may not hav looked at this error if it was a part of a secondary key.
A good example, is an external program that writes lower case data into a CODE field. I had a client once that used ODBC to update thier database directly, and the program put lower case data in Code fields. Everythign worked sort of Ok, since the data was not accessed, and they never used Navision backups, they had some other way of doing it. One day they needed to do a Navision backup restore, and it took me many many hours to find and fix the problem.
At this point I would suggest that they first run a full DB test on their existing database to look for errors, or if possible, backup, and restore a completely new Database using Navision’s backup.
I would suggest though that as a long term solution, you sit with the clients IT people, and find out if they are “Playing” and “Tweaking” the Navision database directly with SQL tools. It could even be a case of them inserting records in a table without knowing how, and say not entering the time stamp correctly, or some other such mistake.