Shipment date in NAV shows the planned shipment date. This date is not when it will actually be shipped but when it is planned to be shipped. Thus, NAV is using this when planning, creating a production order from a given demand ... This shows when sales should be shipped for not being late to customer's needs.
Due date is when production, purchase, transfer, service needs to be done. This due date requires other entity (a demand) which drives due date. As an example, if a demand should be shipped in 2 days from today and we need to manufacture the ítem, the production should be done by tomorrow (1 day earlier if safety lead time is 1D). This is the production order due date.
Posting date is when order is actually posted. This will flow through inventory (as Posting Date column in Ítem Ledger Entries) and will also result in changes on the stock and inventory valuation.
Sometimes we tend to confuse when dealing with the above three dates. To keep it short:
- Due date is calculated from other date (ie. production due date or purchase expected receipt is calculated from its demand requirement/shipment date
- Due date and shipment date are consistent through date conflict functionality in NAV (ie. if a production is specifically required for a demand through an order-to-order binding, the productiondue date cannot be later than demand shipment date)
- Posting dates should also be consistent. Here, NAV offers the "negative inventory" functionality where it allows posting in negative stock. Thus, NAV does not check all scenarios where posting dates are in conflict
The above is interesting when thinking about how date refresh should behave. As an example, what if ...
- Item with lot-for-lot
- We have a demand for Sept 1st
- We do not have capacity in Aug
- Should the production due date be Aug 31st or Aug 1st?
The above is a relevant question since setting one due date or the other might mean not being able to group other demands within same replenishment. Thus, even this sounds a dummy topic (these are just dates, uh?), it is important to understand the differences and consequences on setting one or the other while it is also good to avoid the very frequence confussion with (planned) shipment date (versus what was the actual shipment date).