I did all of that, i put the timeframe on April 1st.
Than TM went back in time, made a copy of the Library.
Than i was told that there allready existed a file with that name, and if i wanted to keep both or overwrite?
I chose for overwrite.
When i reopenend my Calender, i still could see everything wat as written until today, and the two "lost" agenda's didn't reappear.