Many thanks for that response. I was aware Vista doesn’t support TRIM and that was why I was trying (hoping) to use Sandisk Dashboard to run its version of trim manually. But the system BIOS on my old motherboard reports only a SCSI drive to Vista and Dashboard still doesn’t have a solution for that apparently. (they’ve been asking for this to be fixed for over a year in other posts)
I will give those commands a try when I log in next (remote machine), but if all else fails I’ll rely on inbuilt SSD garbage collection and occasional trim using a Live CD of Linux which, I eventually discovered, can be configured to trim NTFS partitions using the latest version of ntfs-3g and fuse components. I tried this on another system and it does in fact trim the NTFS partition. 
