Proc import for delimited files has an option GUESSINGROWS that tells the procedure how many lines to examine before assigning lengths and types to variables. Without the option SAS only examines the first 20 rows or so by default depending on system options.
Use a largish value like guessingrows=32000 to have a better chance.
I recommend this for any Proc Import call where available. Note that large values may increase processing time but the tradeoff may be worth the reduced recoding effort.
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