We are a multi-national corporation with three main distribution centers for export. Currently, we have set up three sourced from codes in the Branch/Plant Relationships for all the importing branches. This has a standard lead time based on average transit time. Exceptions have worked because we've managed outside the system and/or carried extra safety stock. We are trying to find ways to use the system to become more JIT.

There are a few issues we are encountering that I'm not sure how to address:

1 - We have product categories that require testing on inbound. Increasing the standard lead times means carrying more inventory for all our products. But, I don't know of a way to add additional lead time to an item with a Sourced From code.
2 - We have items that are standard air shipment items due to quality. Using the standard lead times means we automatically carry more inventory either at the importer or exporter.
3 - Our transit is not consistent. MRP assumes the shipments will be sent on the day it's planned, but the next shipment may not be sent for weeks. Is there a process to

As there are nearly 9,000 items spanning multiple markets, I'm trying to find a relatively easy way to maintain the lead times. Some ideas that I have thought of:

1 - Using unique sourced from codes for categories (testing, airshipment, etc.)
2 - Using Lead Time Offset - we set up BOM's for kit SKU's so I'm wondering if this will work for finished good planning. Additionally, is it possible to use negative lead time offset for items to deliver later?

If anyone has ideas to address one or more of these issues, I would appreciate the advice.