In the configs for vehicles and weapons (including attachments), the DLC property is often missing or falsely flagging as a DLC for a number of items.
This issue makes it impossible to write a UI script that can show required DLC for items a player is about to purchase or choose.
An alternative solution could be adding a script command to query what DLC is needed (Steam ID or CfgMod name) for a given classname or config entry.