You can do this without nested conditionals by using 1) multiple conditional processes and 2) slightly more complex conditions.  Instead of nesting the conditional processes, you need to repeat that "outer" condition as an if all of the following are true  condition before each of the other, more specific conditions.

Pseudo-code Example
Conditional 1
    if all of the following are true
        If lookup data was not found when using data_x
        If data_x has invalid characters
    Remove invalid characters and retry lookup
Conditional 2
    if all of the following are true
        If lookup data was not found when using data_x
        If data_x has too many characters
    Truncate data_x and retry lookup