Purchase Orders (and its Inventory) are segregated by Inventory System -- and, within any Inventory System, it is possible to further separate Purchase Orders... namely, by P/O-Type.
Purchase Order Numbers are (therefore) unique by P/O-Type within Inventory-System.
Inventory System - Select an appropriate Inventory System.
P/O Type Code - Create an appropriate abbreviation Code for the P/O Type -- for example 'F' for Food/Beverage related PO's.
Description - Create an appropriate Description for the P/O Type.
Examples (within a typical Food/Beverage Inventory System) might include:
Consequently, since PO's are in general segregated by Inventory System, Purchase Order (PO) numbering might follow guidelines similar to the following:
Food/Beverage Inventory System -
PO-Number W-000001 is PO #1 of Wine-PO's within the Food/Beverage Inventory System
PO-Number W-000002 is PO #2 of Wine-PO's within the Food/Beverage Inventory System
PO-Number W-000003 is PO #3 of Wine-PO's within the Food/Beverage Inventory System
PO-Number SUP-000001 is PO #1 of Supplies-PO's within the Food/Beverage Inventory System
PO-Number SUP-000002 is PO #2 of Supplies-PO's within the Food/Beverage Inventory System
PO-Number SUP-000003 is PO #3 of Supplies-PO's within the Food/Beverage Inventory System
PO-Number F-000001 is PO #1 of Food-PO's within the Food/Beverage Inventory System
PO-Number F-000002 is PO #2 of Food-PO's within the Food/Beverage Inventory System
PO-Number F-000003 is PO #3 of Food-PO's within the Food/Beverage Inventory System
Retail Inventory System -
PO-Number M-000001 is PO #1 of Wine-PO's within the Retail Inventory System
PO-Number M-000002 is PO #2 of Wine-PO's within the Retail Inventory System
PO-Number M-000003 is PO #3 of Wine-PO's within the Retail Inventory System
PO-Number SUP-000001 is PO #1 of Supplies-PO's within the Retail Inventory System
PO-Number SUP-000002 is PO #2 of Supplies-PO's within the Retail Inventory System
PO-Number SUP-000003 is PO #3 of Supplies-PO's within the Retail Inventory System
PO-Number S-000001 is PO #1 of Sundries-PO's within the Retail Inventory System
PO-Number S-000002 is PO #2 of Sundries-PO's within the Retail Inventory System
PO-Number S-000003 is PO #3 of Sundries-PO's within the Retail Inventory System
PO-Number F-000001 is PO #1 of Fashion-Accessories-PO's within the Retail Inventory System
PO-Number F-000002 is PO #2 of Fashion-Accessories-PO's within the Retail Inventory System
PO-Number F-000003 is PO #3 of Fashion-Accessories-PO's within the Retail Inventory System
Note that P/O F-000002 [for Food Purchases] from the Food/Beverage Inventory System is uniquely-different from P/O F-000002 [for Fashion-Accessories Purchases] within the Retail Inventory System -- as they are differentiated by Inventory-System affiliation.
In practice, it may be better to use completely different P/O-Type Codes across all Inventory-Systems... just to avoid confusion (even though internally they are unique).