Does any data go into SSD from bootable OS USB (besides OS itself)?
If you used installed OS X on your SSD from a bootable hard drive partition that was cloned from an install DVD, nothing else residing on your hard drive will be copied over without you knowing about it.

The only time user data is copied over onto a new drive is when transferring from a Time Machine volume or a disk in Thunderbolt/Firewire Target mode - something that cannot happen without your knowledge or consent.