I have had a couple of support calls recently that have dealt with document dates that were completely invalid - one for the year 3013 and one for 1944.
Because these had posting dates that were batch related, the transactions went through fine. What this does impact is aging, payment terms, whether they appear on statements or are picked up in payment batches. Yes, we can fix it in the tables, but there is a lot of checking that has to go into it and you can't always be gauranteed to get all fields. Ideally, you don't want it to happen in the first place.
We have highlighted the Professional Services Toolkit in the past and also told you that this toolkit is free of charge now. One of the features is "Doc Date Verify". Once you check the box, this will then pop up a message if a date is entered into a transaction date field this is not a valid financial period. It is looking for whether a period exists in the Fiscal / Financial Period set up window.
If you haven't set this toolkit up in your system yet, you really need to get it in. It doesn't take long to install and register and once in, you have a huge toolkit at your disposal. Contact our support team for more information.