You probably noticed that the DTCC has purged notices in 2008 and before. For example TMMI, AGWS, DGIN (DGIND). DGIN is interesting due to it has been restricted not only back in 2008 and was one of the few stocks that managed a restore of services (I just happened to note it on XL before purged), has done several large RS since then, but then got restricted to T4T again on November 10, 2011 (CUSIP 25536L202 ). Then recently has done a reorganization to "The Automotive Resource Network" and RS again (DGIND) and now has a new CUSIP and ticker as of 2/6/2012 (ARNH, CUSIP 053304101 ). Will be interesting to watch to see if DTCC will be coming in with a notice for restriction of the new CUSIP.
I'm not sure if the DTCC will have a standard number of years before purging public notices, or if it was just a particular instance recently.