HI
Symptom
When is the price list of the Last Purchase Price updated?
Cause
Functionality Description
Solution
Last Purchase Price List:
The prices in this price list are updated automatically by the system when the following transactions are performed:
1. When you enter an incoming invoice, see Purchasing
2. When you enter a goods receipt, see Goods Receipt
3. When you enter a positive opening balance/quantity for an item, see Inventory and Stock Postings
4. When you enter a positive inventory result that triggers a goods receipt, see Inventory and Stock Postings
5. Standard production BOM:
On perpetual inventory system:
When completing production order and receiving the BOM to warehouse (WH) the BOM's last purchase price is updated with the BOM cost in the related inventory posting.
In case the BOM is of FIFO/MAP, last purchase price is updated with total sum of components' costs.
In case the BOM is Standard, last purchase price is updated with the BOM standard price.
On non-perpetual inventory system:
When completing production order and receiving the BOM to WH, last purchase price of BOM is updated with the BOM price in BOM definition.
Disassembly production BOM:
On both, perpetual and non-perpetual inventory system, last purchase price of components is not updated when receiving the components to stock.
6. When Landed Costs are recorded. (Note: When adding AP invoice after landed costs document was created, the last purchase price will remain unchanged.)
If none of these transactions have been performed in the system for an item, the "Last Purchase Price" price list will not contain the item.
Only the list of the transactions mentioned above changes the price of an item in the "Last Purchase Price" price list.
Please note that:
Last purchase price (LPP) will never be overwritten by zero price. This rule is valid for all documents which update LPP, including correction and reversal.
When the item price is zero there should be no update of LPP irrespective of whether there are any freight charges.
Even if a business gets some samples for free, their zero price should not affect LPP which is used for setting sale prices/gross profit calculation/etc.
You can refer other price lists to the "Last Purchase Price" price list with a defined factor. You cannot, however, change the prices in the "Last Purchase Price" price list manually.
Hope Helpful 
Regards
Kennedy