CENTWIN defines the start of a century window for determining whether a 2 digit year is considered as 19xx or 20xx. This provided companies with 2 digit years in their data to sort correctly.
CENTWIN=1975 says the century window begins in 1975. Thus year '74' is sorted as if it were '2074' while '75' is sorted as '1975'.
There is also a "sliding-window' option so the window advances year by year. CENTWIN=20 says the window began 20 years ago from now.
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