The Saudis added about $72b to their foreign assets last year. More actually. The Saudi current account surplus was about $95b. But $72b of the rise in their foreign assets shows up on the balance sheet of the Saudi Arabian Monetary Agency. SAMA's bank deposits increased by $2.5b, its holdings of foreign securities by $68.2b.
That is why I thought trying to infer data on the currency composition of Saudi reserves from the BIS deposit data was a bit risky. But don't expect to find much evidence of Saudi inflows in the US data either (The Saudis are one of the Asian oil exporters). This is a case where the debtor and creditor data just don't match.I suspect the Saudis have been major buyers of dollar securities, but have done so through offshore custodians or farmed some of their assets out to external managers, so it just doesn't show up as a Saudi official inflow in the US data.