As far as the UB's go, for the first 5 or 6 volumes of the regular novels, the books continue on with the continuity established in the Grosset & Dunlap/Digest lines where Iola didn't die. But since then, it seems like the only continous thing in the series is ATAC, otherwise since #7 the continuity has been restarted with every book it seems.

If you are looking as to how the continuity goes overall, here's a list:

Frank and Joe Hardy/The Hardy Boys Are: The Clues Brothers (1997-2000, boys are 7 and 8, respectively)

The Hardy Boys (1927-1979)

The Hardy Boys Digest (1979-2005)

**Possible Alternate Universe**: The Hardy Boys Casefiles (1987-1998)/

A Nancy Drew and Hardy Boys Supermystery (1988-1998)/

A Hardy Boys and Tom Swift Ultra Thriller (1992-1993)

**Definite Alternate Universe**: The Hardy Boys Undercover Brothers (2005-)

A Nancy Drew and Hardy Boys Super Mystery (2006-)