Can I still make a claim if I signed off on the closing financials without reading them carefully?

Signing off on the closing financials — accepting the final statement of adjustments or closing balance sheet — generally forecloses disputing the calculation itself once that process has run its course, but it doesn't automatically bar a claim that the underlying figures were based on false or misrepresented information the seller controlled in the first place. Not reading something carefully before signing is a separate problem from the figures themselves having been wrong.

The real distinction is between accepting a number that was honestly calculated from accurate inputs, which is hard to reopen later just because you didn't scrutinize it closely, and discovering that the inputs themselves were wrong or concealed, which is a different kind of claim closer to misrepresentation than an ordinary calculation dispute. Reviewing exactly what you signed, what representations underpinned those figures, and what specifically turned out to be false is the necessary starting point before assuming either that you're stuck with what you signed or that you automatically have a claim.