1. In SmartList, make sure you choose the Search button and change the Maximum Records setting to a number higher than the default of 1000 transactions.
2. In SmartList, in Sales Transactions, are you looking under the "*" topic? That should list ALL transactions under Sales. The "Open Invoices" topic only lists transactions that have not been posted... by default...but since that is kind of a misnomer, that can (should) be changed in the SmartList definition to select those documents that HAVE been posted. (Consider that in Sales Inquiry a posted invoice WILL (should) show up as an "open" invoice.)
3. In Sales Inquiry, be aware of what is ticked in the Include area (Work, Open, History).
4. If those suggestions didn't gt you closer to fine, have you run Check Links? Or SQL procedures to rebuild your indexes?
5. Finally, it occurs to me that, "if it walks like a duck and talks like a duck..." Maybe the installation of SOP overwrote the existing invoices...? Can you check in SQL Enterprise Manager to see if they are there? Or if using Pervasive, using their table inquiry tool? To determine the table(s) to look at, in Great Plains, go to Tools > Resource Descriptions > Tables. I would look at RM20101, IVC30101, and SOP30200, but there are others to look at, too.
Now, on to your last question about suing your consultants... and I apologize for being wordy...
Maybe you should... there are some I would like to sue myself... and clients, too... (We are Great Plains consultants.) But quite frankly, it usually isn't worth it, does absolutely nothing for building a good reputation in our community, and only tends to create stress and line the pockets of lawyers. We try to move on.
Have you given your consultants the opportunity to try to fix the problem? Any judge, I think, would require that the vendor be given the opportunity to resolve any issues to your satisfaction.
In any event, it gives me hope that there is still value in providing good, clean, honest advice... AND in not billing for every second of time we incur. For example, I'm working this Saturday morning "off the clock" researching an issue for a client... and you...
Thinking of the term "overpaid," I'd love to know their fee structure. We have often felt that our rates are too low. We have many expenses that clients do not consider, including those for training and ever-more complex technology... remember that in order to support our clients we have to stay one step ahead on the technology curve. This week, we had to buy a whole new server just to have enough horsepower to demonstrate a single feature to a prospect... and that demonstration only lasted about 10 minutes. But we love it, and our excitement showed. But I digress...
I hope the solution to your problem is as simple as one of these above suggestions... one other avenue could be to contact Great Plains... if it's a bug in the software, they would like to know about it. If it's an issue with data corruption, they can probably help. If it's an issue with a poor consultant, believe me, they would like to know about that, too. They, and we, care. Good luck!