Purchase order for edited products / variants

[enterprise123]

I had a simple product with it's SKU and other details (product with size of 20ml). Now I added variant in the same product - so the simple product became a product with 2 variant options (size 20ml and 50ml). The product with size 20ml has the same sku as it previously had, and 50ml has new sku. I made the same adjustments to many of my products.

Now I have a problem with my older purchase orders, that included products with size 20ml in it. They appear as "deleted items" and I'm not able to even see which products they are. Is there a fix to that problem as i have MANY purchase orders with lots of deleted products in it. This will mess up my analytics and how sure what to do.

I learned that I shouldn't convert the regular products into variants, but not sure how to fix the problem with purchase orders. 

Any help will be appreciated.

Thanks