As far as I know, both are correct.
The YTD function means to aggregate something from the Januray 1st until today, and it's usually used for comparison to last year YTD.
You also have this function in the QlikView itself:
YearToDate( date [, yearoffset [, firstmonth [, todaydate]]] )
Returns true if date falls within the year to date, else false. If none of
the optional parameters are used, the year to date means any date
within one calendar year from January 1 up to and including the
date of the last script execution.
By specifying a yearoffset (0 if omitted), the function can be transposed
to return true for the same period in another year. Negative
yearoffset indicates previous years while a positive value indicates
coming years. Last year to date is achieved by specifying yearoffset= -1.
By specifying a firstmonth between 1 and 12 (1 if omitted), the
beginning of the year may be moved forward to the first day of any
month. If you e.g. want to work with a fiscal year starting May 1,
you may specify firstmonth = 5.
By specifying a todaydate (time of last script execution if omitted),
you may move the day used as the upper boundary of the period.
YTD has different standard and meaning which can differ from company to company.
1. Its Starting Year to Current selected date
2. financial Year to current selection date .
Last year YTD and Current year YTD are for comparison.
I would suggest you to take inputs from the user that in what terms he would like to see "YTD".
and as Mr.Paul suggested use SET analysis for the same.