st: mysterious missing variables after mydate=mdy(month,day,year)

[ABDUL ADAM <bihiabdul@yahoo.com>]

Dear List,

I have a panel dataset where my date is in different variables (month, day, year), I am able to create a single date variable by mydate=mdy(month,day,year). But the thing is after generating this new variable, stata returns (132 missing values generated). I tried to see where these missing values lie? but to my surprise, I cannot find them; even after 
su  mydate if mydate>=. 
I get zero observations. So, I wonder:

1)what can be the reason of stata returning a missing value while the new variable has no missing values?
2)how can I check the observations that have these missing values.

Thank you in advance,
Abdul

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