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None I think, when he came to the ring battle he mentioned something like it's good to see them again, suggesting that they are dead or missing in 20-years later.

Or he could just mean its good to see them 20 years younger. Nostalgia and all.

Edit: Because Lambo came from a parallel world which Byakuran conquers + kills Vongola. This world, however was changed when Byakuran was defeated.