Why is Download from Vanguard incorrect for interest and dividends?

no one can answer this without more details, what's incorrect about it?  From what I've seen in other posts Vanguard did not support TT import for the legacy mutual fund account, only brokerage accounts, if that's the account merge you are referring to.  If you got separate 1099s for these accounts and import only handled the brokerage account then you will likely need to enter the information the legacy mutual fund account manually.

Actually, a single 1099 covering both MM and Brokerage accounts.  Download only included MM info.  I created another INT form for Brokerage interest.  Shouldn't be a problem next year.