| Year | Individual purchases | Institutional purchases | Total items cumulatively purchased by year |
| 2007 | 331 | 0 | 331 |
| 2008 | 700 | 0 | 1031 |
| 2009 | 503 | 0 | 1534 |
| 2010 | 615 | 71 | 2220 |
| 2011 | 735 | 62 | 3017 |
| 2012 | 1019 | 125 | 4161 |
| 2013 | 841 | 95 | 5097 |
| 2014 | 1058 | 2010 | 8165 |
| 2015 | 1273 | 435 | 9873 |
| 2016 | 1108 | 189 | 11,170 |
| 2017 | 1003 | 198 | 12,371 |
| Total items purchased | 9186 | 3185 | 12,371 |