Recommendations to fix an inventory mess?

You've got a friend here, Korfyp.

Thank you for posting and choosing QuickBooks Desktop as your accounting partner. I can help and share some insights about fixing your inventory setup.

I agree with your idea. You can clone your company file, and update/correct your inventory setup. You can only export and import the correct data on the other company file.

Here's how to export items:

1. Click Lists.
2. Choose Item List.
3. Click the Excel tab. 
4. Choose Export All Items.
5. Click Export.
6. Save the data file. For more insights, you can refer to this link: Export CSV files.

Here's how to import data on the other company file:

1. Click File.
2. Choose Utilities.
3. Select Import.
4. Click Excel Files.
5. Continue the prompts. For your guide, you can use this article: Import MS Excel files.

There are also a variety of applications you can choose from our QuickBooks App Store to help you update and sync inventory files.

Please know that I'm still here to help you more about the inventory feature. Just add a comment below. Wishing you all the best!

@Korfyp 

multiple unit of measure is problematic, see this for why
http://onsale-apparel.com/Rustler/tag/um-good-and-bad

thousands of troublesome assemblies - identify the ones that are not needed, change the name to useless for each, that merges them, then set them to inactive to get them off the lists.

I do not play with the data base tables, there is too much chance that a change is going to impact on some previous transaction and orphan it.

best option IMO, do a physical count, value the qty of each item on hand

1. do an inventory adjustment, set all items to zero qty and zero value, use the qty and value type of adjustment, create a dummy bank account called holding and use that account as the adjustment account

2. enter transactions, from the dummy holding bank account "buy" inventory items, qty on hand, and total value of that qty. Use a dummy vendor you set up, I call him inhouse.

3. when you are done, check the balance in the dummy holding bank account, if it is negative, do a deposit and use COGS as the source account for the deposit to get the balance zero. If the balance is positive, your valuation of what was on hand is wrong, you can edit purchases and allocate more money to items that need it until the balance is zero

Thanks for the detailed information, @Rustler and @HoneyLynn_G - all very useful.  If I may elaborate and get more of your feedback:

Essentially, the new owners have zero insight into company financial performance since they took over and installed QuickBooks last summer.  Because the products' costs were incorrectly listed in the initial setup, our average COGS is way, way off (too high) for each product.  What a mess...

Is there any way to correct the costs and recalculate the average COGS for the last few months?  I realize this is likely impossible so as to protect financial records from dishonest editing, but we have a genuine need for this type of change.  Otherwise it seems that we're stuck with those wildly inaccurate COGS averages - and because those averages appear to be permanent, we will never truly have accurate financial reports.  Needless to say, correcting the cost right now has no effect on the average over the past few months.

It makes sense to me that there exists a solution to fix these averages which are causing our reports to be hundreds of thousands of dollars off, but I don't really know where to start.  We weren't exactly trained and left in good hands >:(

@Korfyp 

I know it is a hassle, but the best way to do it and get it right is the way I stated in my other post.

Right on.  I'll take your recommendation to our finance team.  Thanks a lot for your help.