Just to clarify, your M4-P is black chrome? From the table below I pasted from the Leica forum, it seems Leica started putting out black chrome with serial #1546:
Leica M4-P Serial Numbers
SN StartSN EndProductYearBatch
1528651**^ 1533350Leica M4-2 ^1980[4700]
15433511545350Leica M4-P (chrom)19802000
15463511552350Leica M4-P (black)19816000
15623511564350Leica M4-P (black)19822000
15863511590350Leica M4-P (black+Everest)19824000
16045511606550Leica M4-P1982-832000
1618551*1620550*Leica M4-P (13-83.chrom)19832000*
1620551*1622550*Leica M4-P (black)19832000*
1636551*1637550*Leica M4-P (13-83.chrom)19831000*
1642551*1643750*Leica M4-P (chrom)19841200*
1649251*1651250*Leica M4-P (chrom)19842000*
1691951 ^^1692950Leica M4-P ELW (black)1986*770*
Totalassignedserial numbers1981-198624,970**
I have a black M4-P myself with serial #1548. Both top and bottom plates have wear, including a small dent on the top plate (ugh) and has exposed more of “silvering” instead of “brassing.”