Reliable historical data (for indexes)

Hello everyone ! I downloaded QuantDataManager and I have heard that data from Dukascopy cannot be trusted for indexes. It seems that no other provider on the software allows to retrieve data in ticks for indexes. Can someone tell me where can I find a reliable data provider for indexes (S&P, DAX etc.). If so, do you know if these data providers include the seasonal “rebalancing” of each index (quarterely for S&P for ex).
It’s hard to find information on the internet for reliable sources, so thank you very much for your help !!
Have a great day !

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I believe the quality of data among CFD brokers is kind of similar. Each and every broker cooks their own and that’s the reason why it is so. If you ask for disadvantages of using CFD to trade indexes then data issue would be one reason. For that I have always prefered futures trading but we have many users that successfully trade using CFDs. The data quality required highly depends on the strategy used. For simpler strategies data quality with most brokers (MT5) is sufficient