According to my research, the difference lies in the document feeder:
RICOH IM C2010: This model is equipped with an Automatic Reversing Document Feeder (ARDF) that can hold up to 100 sheets.
RICOH IM C2010A: This model has a Single Pass Duplex Feeder (SPDF) with a capacity of up to 220 sheets, which allows both sides of a document to be scanned at the same time, making it more efficient.