We do have complex verification algorithms that constantly monitor the correctness of candles being formed and data supplied. However, as with any of the systems, it might rarely provide truncated values. In such a case, let our support team know about this.
Twelve Data is not affiliated with any other data provider company (e.g. Yahoo, TradingView, WeBull, etc) unless explicitly stated. Therefore, there is no guarantee that the data will match other sources due to the fact of how the data is aggregated. At Twelve Data we use canonical formulas to meet the institutional level quality.
Daily data completely corresponds to officially provided EOD data, as the only thing being announced by exchanges. Intraday and other intervals are calculated from the tick level data and therefore might differ across sources and brokers.