What numbers were given ? Please show because these numbers are for Budokai 3, which is a video game and are stand alone for this video game not the actual cannon series.
Bardock had sparks on him when he first went SSJ, but it was still just SSJ. And again adding Baby inside him and yet again no further forms shown. What you're suggesting is no different than those people who 'suggest' Cell can system bust. Words were said, no evidence was given. I'm going by what we've Seen and what numbers we've been given.
Also like I said GT and animated movies followed different systems. In GT no sparks were ever shown except for that one instant . So you couldn't differentiate a SSJ and SSJ2 which says something about what the animators were trying to convey for that scene.
I've already established a plausible argument that
1. People involved in fusion dance have no memory of what they did when they are fused because the fusion character is a new person as stated by daizenshuu.
2. Trunks and Goten are aware and have recollection of Ultra SSJ as stated by them in the manga. They have no reason to lie. Japanese manga are not american comics in story telling. Authors don't always have to show the actually happen, character statement is enough sometimes.
3. In conclusion it seems to suggest that Trunks and Goten did acquire the Ultra SSJ transformation.