The evidence strongly supports the statement's truthfulness. The most direct and compelling evidence comes from Investing.com, a major financial data portal. The summary for this source explicitly states that a content snippet shows a US Dollar Index value of 99.77, which is unequivocally below 100. This single data point is sufficient to confirm the statement. This direct evidence is further supported by several other highly authoritative and relevant sources. TradingView, Yahoo Finance, MarketWatch, and TradingEconomics are all described as leading financial platforms that provide comprehensive historical data and interactive charts for the US Dollar Index. Their nature as primary data providers for financial instruments means they would accurately reflect any instance of the index trading below 100. There is no contradictory evidence among the provided sources. None of the sources suggest that the index has never fallen below 100. The combination of direct numerical evidence from a credible source and the corroborative nature of other top-tier financial data providers leads to a high degree of confidence that the statement is true.