Here are some Stata code snippets for checking duplicates in your panel data. (I have to figure out how to do this because my panel dataset have duplicates, and therefore I cannot do a tsset on the data) The command to use is duplicates.
To list any duplicate observations, run:
duplicates list
For the duplication issue I have with tssset, I specific the two relevant panel variables
duplicates list termtype dateIndex
Now, to create a dummy variable isdup to mark the duplicates
duplicates tag termtype dateIndex, gen(isdup)
In my case, I just manually remove the duplicates using the graphical editor:
edit if isdup
Or, to just remove it using the command
duplicates drop termtype dateIndex
An example:
sysuse auto
keep mpg rep78
duplicates list
duplicates list rep78
duplicates tag rep78, gen(isdup)
list if isdup