Improve next-year imputation procedure

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RFSD companion paper writes:

It is important to note that we only impute the entirely missing statements. If a value in statement t differs from value reported in statement t+1 it may be due either to a mistake correction or to a change in reporting standards. As it is impossible to distinguish between the two automatically, we leave the not-missing statements as is and do not use the information from t + 1 or t + 2 to correct year-t statements.

This approach results in data loss since firms may correct previous-year financials in their future filings. These corrections are now ignored.