DateTime.Ticks
and FileTime
are two different units.
DateTime.Ticks are number of 100-nanoseconds since January 1st 0001.
The value of this property represents the number of 100-nanosecond intervals that have elapsed since 12:00:00 midnight, January 1, 0001, which represents DateTime.MinValue.
FileTime however are ticks since the 17th century (January 1st 1601) in UTC time.
A Windows file time is a 64-bit value that represents the number of 100-nanosecond intervals that have elapsed since 12:00 midnight, January 1, 1601 A.D. (C.E.) Coordinated Universal Time (UTC).
So your calculation will always miss by 1600 years +/- a few hours.