C is Cleared and would be from accepting a green match in the Review screen.

R is Reconciled and means you have completed a reconciliation that includes that cleared item.

Double entries usually happen when you have entered a transaction manually and then Add from Review instead of matching. Dates are different because the bank feed dates are when a transaction clears. The proper date is the actual transaction date. Example. You write a check on 4/30 but it does not clear your bank until 5/5. The correct date is 4/30 and by adding from the feed instead of actual entry by date you have posted expenses in the wrong month