Well Trunks certainly didn't get any stronger since Vegeta says that at his current level he is still no match for Black. I don't think the other Saiyans would get stronger either. Vegeta is a tactical genius, if Trunks can power up the SSJ2 form than it's definitely for Vegeta to figure how to go beyond that, especially with how powerful he was able to make in BoG through rage.
I am starting to go by Cadaver's theory about none of the Saiyan getting stronger throughout the arc and Black only surpassing God after obtaining Rose and that Blue Vegeta had a lost of yuuki vs Zenkai SSJ Black.
I can see the possibility of an amped Super Saiyan 2 even though there's no mention of it but loss of yuuki? That's purely headcanon and not supported.
As for the topic, Vegeta simply got a lot stronger IMO. The only scene we are shown is Vegeta training with Trunks in the gravity chamber in his Base form. Considering how Goku believed Goku Black would be a tough opponent after battling Trunks may suggest that Black was around God level. Base Goku Black was far above FPSSJ2 Trunks and could go Super Saiyan on top of that which might further be evidence of that.
SSJ2 Vegeta was shown to be overwhelming SSJ Goku Black who was stated to have gotten even stronger from when he faced Trunks. I think the intention was that both Goku and Vegeta had gotten stronger in preparation of Black seeing as how Goku was explicitly shown to be meditating during the same time as Vegeta's training. Therefore, I believe this is suggested:
SSJ2 Goku/Vegeta (Post-Training)> SSJ Goku Black (vs. Vegeta) > SSJ Goku Black (vs. Trunks) ~ SSJG Goku (vs. Trunks) > Base Goku Black (vs. Trunks)
You could make an argument that Base Goku Black may have been on par with SSJG Goku since he made FPSSJ2 Trunks look like nothing but that's likely overkill. Trunks was able to fight against Base Goku Black to some extent whereas SSJG Goku absolutely one-shotted FPSSJ2 Trunks. SSJ Goku Black should definitely be able to one-shot him which falls in line with the above chain.