Your code carefully trimmed leading and trailing spaces. To be sure of the sort working on the strings you might also wish to ensure: that each field is the same width; that 1 digit values had leading zeros or spaces consistently; that the separators were consistent; that the spacing was consistent; and so on.

By the time you've done all that, it might be more straightforward to use a function a convert text dates to numeric dates, which would smooth out format variations for you !