that is just diff adjustment at work. I've written a small tool to summarize diff/network size.
These are the sliding 1-day-average numbers for network size in PB for the last fortnight:
14: 24.702
13: 26.0253
12: 24.8066
11: 23.7753
10: 24.5259
9: 27.2328
8: 25.823
7: 24.7602
6: 24.218
5: 24.5997
4: 24.0262
3: 30.4774
2: 23.7803
1: 26.9724
and sliding 1-month-average for the last three months:
3: 14.8088
2: 20.388
1: 24.6363