I cannot completely follow you, but your number of 17.2 Trillion is off by the factor 1.000, and the fortune of the Rothschild family spread and resolved from generation to generation, as large family fortunes always do.
In 1816, the GDP was 0.32 billion pounds. If you assume from 1816 the lending to UK govt bonds was the Rot Schild bank, the starting point of the Rot Schild base moeny that I took will be far more than USD 1 million. So I think you will arrive at a trillion any which ways.
The reason for this is that from that year going forward, the Rot Schild would have bought bonds from the govt (effectively lending them money) every year going ahead, giving them (the Rot Schilds) a passive income stream from then to now.
Each year a new income stream would have been added by loaning additional bonds, which was independent of the previous years income.
I don't know what numbers to plug in, perhaps that is left to someone more knowledgeable than me.
