Same concept for reading - threshold regions indicate multiple bit values, but different for storage.
The 8087 used physically different transistor sizes[0] to read a voltage level that "stored" two bits inside four threshold regions. MLC/TLC/QLC/PLC use a single transistor but charge the gate to a different "analog" voltage that is between 2^n threshold regions - MLC has four (two bits), TLC has eight (three bits), QLC has 16 (four bits), and PLC has 32 (five bits).
The 8087 used physically different transistor sizes[0] to read a voltage level that "stored" two bits inside four threshold regions. MLC/TLC/QLC/PLC use a single transistor but charge the gate to a different "analog" voltage that is between 2^n threshold regions - MLC has four (two bits), TLC has eight (three bits), QLC has 16 (four bits), and PLC has 32 (five bits).
[0]: https://www.righto.com/2018/09/two-bits-per-transistor-high-...