Round 4 Why are there so many unmatched Symbols?

I got 288 predicted values for round 4 and 12 NA values that I imputed (took an average of the prediction indicators). My results were below
my expectation, possibly from the amount of NA's. Is this common?

Answers and follow-up questions

Answer or follow-up question 1

I answered my own question. We had a variable including return over a 12 month period, and some variables don't have 12 months of data. Our
code dropped all NAs so 18 stocks were dropped since they started during the year and don't have 12 months worth of data. For the future we
will create shorter time length for returns, or not use this variable..

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