(B) the net wealth assessed under section 17, where assessment has been made under that section, as reduced by--
(1) the net wealth, if any, assessed previously under section 16 or section 17, or
(2) the amount specified in sub- section (1A), whichever is greater,] but not exceeding, in the aggregate, an amount equal to the net wealth assessed under section 16, or, as the case may be, the net wealth assessed under section 17, as reduced in either case in the manner aforesaid;