Job Plan Material Costing Logic

When creating job plans, and planned materials are added, we've observed the following:
1) If Direct Issue is left unchecked, and storeroom not filled in, the unit cost is zero
2) If Storeroom if filled in, then unit cost is populated per the storeroom cost details.
3) If Direct Issue is checked, then the default vendor for the item (if one exists) will be added to the line along with the default cost. If there is no default vendor for the item, then the unit cost remains at zero. If the user changes the vendor to match one of the records on INVVENDOR, then the unit cost will update accordingly.

However, in practice we've found the following:
1) More commonly, the vendor(s) for an item are added later, so at the time of job plan creation, the vendor is unknown. If then vendor is left null, then there will never be a material cost for that item, either on the job plan or any related PM. The cost will only be applied when the job plan is added to a WO, when the INVVENDOR rules are applied (contract, then default, then last date, etc.)
2) Even if the vendor is known at the time of job plan creation, the Supply Management group is constantly updating vendors (adding new, removing old, apply default vendors to items). The result is that on the job plan, the vendor originally specified may no longer match an INVVENDOR record (resulting in a zero unit cost), or the vendor on the job plan no longer matches the default or last user vendor from the item, resulting in old information on the job plan. Either way this results in inaccurate costing on the job plan and related PMs.

A preferred method is to leave the vendor null on the job plan, and let the INVVENDOR rules apply the correct vendor and costing on the WO when the job plan is applied. While this works great for the WO, it results in inaccurate costing on the job plan and related PM forecasting.

One particular client has over 100K job plans, and uses job plan revisions, so it's not possible to revise job plans to change vendors as changes are made on the item. In addition, since the job plan details take precedence, you can get situations where disqualified or unused vendors (which were added to the job plan years ago) are defaulting on WOs when the job plan is applied.

The expectation is that the INVVENDOR rules would be applied on the job plan the same way they are on a WO, which would ensure the job plan costs are accurate, as well as the associated PM forecasts.