Maybe it was a typo but there is no Win2k SP5. The last one that was produced was win2k SP4 unless I am missing something.
There are unofficial service packs out there for various WinOS, including Windows 2000. Heck, there are several unofficial service packs for Windows 98 SE, up to version 2 last time I checked.
People like to believe once Microsoft discontinues support for a certain OS that fixes and patches stop. It don't work that way. There are millions upon millions of developers, businesses, regular and power users out there who depend on and actively use "older" WinOS releases. Example: MSFN forums has a huge Win95/Win98/Win98SE community. They even got some kind of project going for patching the kernel and various libraries/DLL's on Win98 so it would run Win2k/XP games/apps.