Note that there are two Dow Jones Industrial Averages.
One is the "theoretical" version in which all constituent stocks are assumed to have made highs and lows simultaenously during the day.
The other is the "actual" version in which all constituent stocks are sampled intraday on a real-time basis and the highs and lows represent the "tick high" and "tick low" of the DJIA.
Dow Jones only started officially calculating the actual version in 1992.
Perhaps that might explain the differences.
Also, watch out for:
Saturaday trading - the NYSE traded on Saturdays until the mid 1950s so your DJIA should have that data.
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