Ive seen DSA 100 and DSA 102, now where is DSA 101?
Several vendors (mostly of GNU/Linux, but also of BSD derivatives) coordinate security advisories for some incidents and agree to a particular timeline so that all vendors are able to properly determine if they are (or not) vulnerable and create the patchs needed. The Debian Security Team holds, in this case, the numbers before the advisory can be released, and hence temporarily leaving out one or more advisories by number.