Do it for as many times as you want.
This device was stored securely in a fire safe at home, not used as a portable device.
Where do you think the drive will keep data after saving an amount of data multiple times the size of the drive?
What you describe might happen if you "delete" a file and save a new one. Then it is most likely recoverable.
Overwrite you whole SSD 10 times I doubt anyone but the most serious attacker can find anything, and even then.