Well, as I already told you, from my idea, Ivan (or other) steals the reward or treasure of the quest of 100 years, the team of natsu + laxus leaves looking for him.
Gyldarz talks about his 100 years quest + his relationship with Ivan how he was before.
1-2 tome it is not sufisant for the continuation T-T, minimum 4 tome.
If blue mistral, fairy girl, ice trail we had 4 tome, this must do the same +.
The spin off of sting, rogue, laxus and gajeel, was only 1 volume each because it was a story annexed to them.
Same for the FT zero.
But the fact that it is the following offfciel manga, 1-2 volume is 20 chapter is not sufisant at all.