@Akervin 

I'm not sure if this is answering your question but try going to Settings > Products and services.  Click the filter (funnel) icon and under 'Type' select Inventory.  Then click the 'Batch actions' drop-down and select 'Adjust quantity'.  That will allow you to adjust all 1,617 items on one screen using the same inventory adjustment account.  You can try other filters as needed to make it more manageable.