I have a SanDisk X300 2.5 7MM 256GB in my laptop with FW X3520012 currently installed.
When I check for firmware updates using SSD Toolkit it tells me there are none available, however I know that there is a X3540000 update as documented here: http://kb.sandisk.com/app/answers/detail/a_id/19261/
There is a manual update option but I cannot find a download link for the firmware?!?!
the ssd toolkit is not working anymore and is end of life software. so in that case i suggest using the ssd dashboard that will show up the correct information of the ssd
in that case there are 2 options left. It can be that you are using an OEM drive that was built inside the computer and is using another firmware that came with the pc
or
the firmware listed on the documentation is not correct
Thanks for sharing this information with us. This was really useful to me. I am waiting for more updates from this admin. Keep continuing as much as possible.