For everyone that would worry about hand notes on their notice to appear to take citizenship test:
The mystery was clarified.
St. Clair office has an internal process that assigns each person invited to take the test to a certain clerk that runs interview/papers check after the test.
In the day I had the interview people had pink papers handwritten with A to E letters. There were 5 clerks in the large room, each of them taking care of only people having same letter on their invite.
It seemed the officers were already familiar with each case assigned to them.