PS The events described in Sections 2.1 and 2.2.1 of my post are listed below in date order.
(1)
26 February 2007 The image of the word age was written on a scrap.
26 February 2007—28 February 2007 The experiment in which there was the scrap with the image of “age” written on it.
28 February 2007 The scrap with the image of “age” written on it was taken away.
(2)
8 March 2007—15 March 2007 Experiment 1.
(3)
28 March 2007—5 April 2007 Experiment 2.
5 April 2007 The scraps used in Experiment 2 were taken away.
(4)
10 April 2007 The image of the circled letter S was drawn on a scrap.
10 April 2007—15 April 2007 The experiment in which there was the scrap with the image of the circled letter S drawn on it.
(5)
18 May 2007 The dark watermark-like image of the word "age" was found in the upper scrap used in Experiment 2.
27 May 2007 The light watermark-like image of the circled letter S was found in the upper scrap used in Experiment 2.

Best of luck from Zhang Xu