If I run Belarc Advisor on my XP Home computer (which doesn't have SP3 installed), it lists a number of recent patches under the sub heading 'SP4', as per this list;
"SP4
KB938464 on 09/09/2008 (details...)
KB946648 on 12/08/2008 (details...)
KB950760 on 11/06/2008 (details...)
KB950762 on 11/06/2008 (details...)
KB950974 on 12/08/2008 (details...)
KB951066 on 12/08/2008 (details...)
KB951072-V2 on 12/08/2008 (details...)
KB951376 on 11/06/2008 (details...)
KB951376-V2 on 08/07/2008 (details...)
KB951698 on 11/06/2008 (details...)
KB951748 on 08/07/2008 (details...)
KB952287 on 12/08/2008 (details...)
KB952954 on 12/08/2008 (details...)
KB953839 on 12/08/2008 (details...)
I have checked the details of a couple of these patches and they both appeared to be Critical ones. It is definitely correct that no single SP4 has been issued by MS, so I have no idea why this particular group of modern patches (which most people will have obtained separately in the 'normal' way from Windows Updates) should have been gathered under the SP4 sub heading, unless this is some odd convention used by Belarc. (There is also a small group of patches gathered under the sub heading 'SP 0', so this may support the idea that these categories are purely a Belarc thing)
What I can say is that, to the best of my less than reliable memory, similar sub groups seem to have been present in most Belarc scans that I have run previously, although I have never paid them much attention before!