QuoteSamsung rates the 980 PRO for up to 1.5 million hours of use, for example, or 300 TB of total writes.
You can't say 300 TB written without specifying the capacity. Because those figures are a function of capacity. It's better to say that it's rated for 600 complete rewrites. Which tells you that 300 TB value belongs to the 500 GB version. 2 TB version is rated for 1200 TB.
You can't interpret MTBF this way. It claims to be an average time, meaning some can do better, some worse, across a statistically significant pool of units. But as always, devil is in the detail. Do you really believe someone tested one of these for 1.5 million hours? That's impossible. It's over 100 years. The common way of doing this is to take a whole bunch of them, test them for a given amount of time (a month, for example) and calculate MTBF as #units * time / #failures. If you run a thousand units for a thousand hours (that's about six weeks of 24/7 testing) with one failure, you've got MTBF of one million hours (1000 * 1000 / 1). You don't have to be a genius to realize that testing something for a thousand hours is a very weak evidence for it lasting a million hours. The test can involve accelerated aging - essentially, subjecting the devices to abuse which should significantly shorten their lifespan and expose problems. But the only way to really know whether something will last ten years is to run a significant number for ten years. And that's not practical if you want to deliver a product to a market. So, one needs to be careful with MTBF as a number. You really need the details to make it useful.