I've read that SSD's will lose data if left unpowered for long periods but I left my old Samsung 850 Pro 128GiB unpowered for two years or so and it still retained all the data.Not to mention cold offline storage.
I have a bunch of 2,5 Inch HHDs in USB enclosures to backup files. I'm not gonna do that on SSDs, as it's just not safe for long time.