I take it you were looking for SAS/C patches on aminet:
http://wuarchive.wustl.edu/~aminet/biz/patch/index.htmlsc6_3.lha there is a bug fix for 6.0-6.3, but I assume you have already seen that.
I have SASC 6.50. The patch disk for 6.50 to 6.5.1 readme states that Version 6.50 is required to have been installed. This patch was included as the 7th disk in the set. I then patched 6.55 to 6.58 using the above link from aminet. I bought mine years ago and the manuals are for Version 6.0, although the Disks are 6.5 and dated 1 Oct 93. My disk 1 readme states that there is no manual for 6.5.0 and that users should use the 6.0 Manual. I have not come across any major problems so I don't think you are missing out on anything. The biggest headache I ran into was cross debugging with CPRX over 2 amiga. Version 6.5.8 seemed to make it more reliable and less prone to crashes.
The list of changes from 6.0 to 6.5.0 is not as extensive as the 6.5.1 patch. The biggest changes seem to be with bitfield structures in 6.0 not being compatible with SASC 5.xx. The 6.5.0 bitfields were again changed and were not compatible with 6.0. The 6.51.1 patch has an extensive list of changes, as well as reverts the bitfields to be compatible once again with 6.0.
You still use SAS/C? I thought I was the only one in the universe that did...