Lately, I've been trying to complete the "offline" part of the game since I stoped playing the game years ago out of pure boredom and I still had some aircrafts to fill their kill gauge. So, I decided to do this, but there are several ones that, even with the kill gauge at 100%, I can't buy their special weapons because they have not unlocked. Depending on the plane, only one SP WP would unlock. On others, no SP WP would be available for purchase, even with the kill gauge at 100%. I have also completed all the missions in all dificulties with S rank and got all medals except the one given with all the emblems, colors, WP and aircrafts bought.
Could this be because I NEED to play multiplayer in order to unlock these SP WP?
If it helps, the planes which I have this issue are (still need to fill the kill gauge of some more):
F-4E (only one SP WP unlocked)
F/A-18E (only one)
F-5E (only one)
F-16C (no SP WP unlocked)
SU-27 (only one)
SU-47 (no SP WP unlocked)