Reopening assessments: tax charged as if omitted income had been originally assessed; claim can stop proceedings if original assessment stands. Tax in reassessment, recomputation or assessment for escaped income is charged at the rate or rates that would have applied had the income been originally assessed. An assessee may have proceedings dropped by claiming the original assessment was not lower than the correct liability and by not having challenged the original assessment order; succeeding on such a claim bars reopening matters concluded by prior assessment-related orders.