Change in Sales Order Value 2 years later

I have a sales order that was processed in 2018 originally for $302K that contained services and products. Two years after the sales order was processed and partially invoiced (50% upfront for services), we had a list price change for our services where some of the service items had a reduction in price. NetSuite changed the list price on the sales order to reflect the new price and not the price that was originally saved and invoiced.

When we completed the billing, the second invoice was at a different rate than the original. NetSuite support says this is normal, but I can't think this is normal behavior. I would expect approved and partially billed sales orders would have their values locked. What am I missing here? The price changed 2 years after the Sales Order was created. I don't think this is preferred behavior, I have not noticed this happening to other items but now I am afraid. The revenue committment still shows the full value as processed, how does this not screw up deferred revenue?