Need more knowledge !

Valiant Premium Convertible...

P4B = premium front bucket, vinyl, Blue.....Looks like you may have a recovered seat as the originals in my 65 were very flat. Man that would be a weird combo for a vert? Moisture.....? That would likely be a P2B or P8B code if original.

T=L low grade trim bench (buckets on Polara, Newport 2-dr H.T.)
T=M Medium grade trim bench
T=H high grade trim bench
T=P premium front bucket seat
T=T taxi (bench)
T=K police (bench)
R=1 cloth + vinyl
R=2 cloth + vinyl (low + police)
R=3 Leather
R=4 vinyl bucket seats
R=5 vinyl bench seat 2 dr. sedan and 4 dr. sedan and hardtop
R=6 cloth bench seat (4-dr H.T Imperial)
R=7 cloth and leather
R=8 vinyl + cloth seats 2+4 dr. sedan (vinyl on Fury I)
R=9 Special order (Leather and special order)
M=A gray
M=B blue
M=C blue and white
M=G green and gold
M=L gold and black
M=N black and white
M=P gray and black
M=K purple
M=Q turquoise
M=R red
M=T tan
M=U black and copper
M=W white
M=X black
M=Y white seats + headlining + gold carpet (Dart) all others Gold
M=Y White seats + gold headliner + carpet (Coronet) all others Gold
M=V red and white

http://earlycuda.org/techdocs/6265FenderTagDecode.pdf