Are you sure? This piece of information has very serious implications.
It does make sense though:-
SLC: 2x voltage states =
0: (0v),
1: (100%) of whatever voltage it's programmed with
MLC : 4x voltage states =
0: (0v),
1: (33%),
2: (66%),
3: (100%)
TLC : 8x voltage states =
0: (0v),
1: (14%),
2: (28%),
3: (43%),
4: (57%),
5: (71%),
6: (86%),
7: (100%)
With small process nodes there are far fewer electrons holding each charge, so it "trickles out" quicker when unpowered. With TLC, a voltage drop of say 5% from state 6 would mean 81% instead of 86% of the charge is being held. If it's then powered on, the ECC could correct for it as it's obviously above 71%. However, SSD firmware can only correct voltage drift when it's powered on. If it's powered off for too long and the voltage fell by say 15% (86% to 71%), the "drift" will be into the next voltage down (and the data corrupted), at which point how can the SSD tell if "70-72%" is a "good 5" or a "badly drifted 6" state? Meanwhile, the same 15% drop is still readable on an MLC (66% to 51%) with a great deal more headroom to spare.
Everyone keeps talking about
this chart whenever the subject comes up, however all that data is based purely on Intel's "accelerated testing". It's also obviously going to be radically different depending on technology (MLC vs TLC) and process node (16nm, 19nm, 40nm, etc). Given that it's Intel drives used in testing, I have a suspicion all that data applies to Intel's MLC drives, so those figures are obviously going to be lower for TLC which has less than half the headroom for unpowered "voltage drift" when used as mostly offline storage.
Despite the "promise" of 40nm 3D-NAND to have fixed things, I'm personally steering well clear of TLC drives from all brands. It's not as if Samsung's TLC EVO's are massively cheaper than Crucial's MLC drives, which is after all the only advantage TLC has (or is supposed to have...)