I noticed quite a while back that when I update CCleaner the 'Installed On' date in the 'Uninstall or change a Program' window does not always change to the new install date like it does for many programs. Since I normally install the new version on top of the old version I figured that was why but today I completely uninstalled the previous version before installing the latest version and the 'Installed On' date is showing as 12/19/2012 which I believe is when I last updated CCleaner. I am not even sure where it got the date from since I uninstalled it first, ran Disk Cleanup and checked the registry before installing the new version. Recuva and Defraggle show the date they were actually installed on, even when just being updated.
This issue started with version 3.19.1721 when I installed it on 5/30/2012 and the "Installed On" date in Windows Add/Remove Programs Control Panel showed the install date as 5/23/2012. It has not been right since then.
Actually that means that on almost all programs that I update they all change the 'Installed On' date to the actual date of installation. CCleaner always did too in the past. I have quite a few programs installed and I am sure there are a few that do not change the installed on date when they are updated but that is because they were not implemented with that option.
I actually saw this when doing a clean install of Vista on a machine last weekend, (the drive had been wiped first). All programs in Programs and features were listed as installed on the date I did it, apart from CCleaner which had that December date.