Here are some code 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