Mitsubishi Electric Mr.SLIM PEA-M250LA Manuel D'utilisation page 139

■ The serial number is indicated on the SPEC NAME PLATE.
Sequential number for each unit: 00001–99999
Month of manufacture: A(1), B(2), C(3), D(4), E(5), F(6), G(7), H(8), J(9), K(10), L(11), M(12)
Year of manufacture (western calender): 2014 → 4, 2015 → 5