Hi. I created a simple dataset with a few missing values, ran MULTIPLE IMPUTATION, then DESCRIPTIVES on the imputed variable, and everything worked correctly, where by correctly I mean I saw this:

Notice the "Pooled" row at the bottom of the table. Other pooled statistics are available depending on the procedure you are using.
You don't designate values as imputed; if you look at the MI dataset, you will see that imputed values appear in highlighted cells, for example:

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Rick Marcantonio
Quality Assurance
IBM
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