My first job as a freelancer, was for a client that had been refused an audit, by this I mean their accounting company refused to sign off the accounts because they could not prove the numbers. Key to it was the Cost Of Goods Sold. Basically without the sign off they were in for a huge tax bill, and it went back three years, so there were also going to be some stiff fines if they could not prove the numbers. The company had ben audited before by a small accounting company, but now they had grown to the point where they had to have an audit signed off by one of the Big 7.
It took me about 9 weeks, of very long days to do the job. Working at nights, and updating live data during the night as I corrected cost issues. But ultimately what the Auditors needed was a print out of every GL entry in the COGS account, and an audit trail of why it was there, and justification that it was a valid COGS.
Eventually I had the report, we bought two new big printers, and shut down on Friday afternoon and started printing through the weekend. The company had one guy working the weekend whose sole job was to feed the printers. Basically form the shut down, the company were not allowed to touch Navision until the auditors had signed off. We finished printing late Sunday night, and put the report in those vertical Document holders, with the from to date marked on the outside. The final printout was just short of 4 meters long/high which is a lot of paper.
Monday in came the Auditors, the head Lady iin charge, and 3 of her juniors. She told them to grab one page each at random. She took the three pages, glanced at them and said “yes this looks fine, you can restart the system now”.
When I asked her latter, she said that basically if we went to all this work, and we trust the numbers, then all she needs to figure out is if she can trust us. Which now she did.
The point is that these AUditors are not stupid, most of them have seen all the tricks, they just need to know that you understand your system, and are able to work with it to get numbers you trust.
You just need to get your people to understand Navision. And in any case an entity diagram wont help in the tiniest bit. Instead, learn Navision, learn the system, and when they ask you questions know how to work out the correct answer. If you trust your system, then you just need to get them to trust you.