Vegeta and Trunks mastered Super Saiyan during the Cell Games

[DBZAOTA482]

They're not morons so they definitely took a page out of Goku's book and mastered regular SSJ, but they lacked the benefit of newbie gains like Goku and Gohan so they were still far weaker after their 2nd trip to the RoSaT.

Cell Jrs were said to be similar to Perfect Cell in power yet Vegeta and Trunks were the only ones able to hold their against them when they were attacking them to make Gohan enraged.

 

[SSJ2]

It begs the question then, why wouldn't they have been Super Saiyans in their natural state? Vegeta said that normalizing the form would greatly reduce its strain and yet he still showed up to the Cell Games in Base.

I think you can argue that they partially mastered the form given how much stronger they became, but they lacked the traits associated with full mastery such as the softer eyes and the FPSSJ aura.

 

[Dagon]

It begs the question then, why wouldn't they have been Super Saiyans in their natural state? Vegeta said that normalizing the form would greatly reduce its strain and yet he still showed up to the Cell Games in Base.

I think you can argue that they partially mastered the form given how much stronger they became, but they lacked the traits associated with full mastery such as the softer eyes and the FPSSJ aura.

Soft vs angular eyes is about mood more than it is about the form. Vegeta and Trunks would still have angular eyes if using precisely the same form as Goku and Gohan. It's their character trait.

 

[Hector]

They were Semi Mastered Super Saiyans.