I've been trying to summon a certain warsaw pact firearm, but when I put in the ID from the GECK, the console comes back with an error, saying the form_id doesn't exist. I tried using the prefix for 20thcenturyweapons.esm before the id, like with items from DLC, but it still did not work. I am inputting all necessary values (amount, condition) and am not making any mistakes in the typing of both the command (player.additem) and the object ID (in this case, 020184DC). I have this same problem with all other weapons from this pack, but I can obtain any vanilla object with no issues.
Any fixes/theories would be welcome.

To be 100% sure whether you're using the right ID, open your entire load order with FO3Edit, find the item in question and look for it's FormID.