Might be a good idea to start logging these letter codes and see if a pattern emerges?
A:
1978 ST100N. Neck: Not known, Body: 4=4 N A, (SN 0000276)
1978 ST100 OW. Neck: 8000720, Body: ST100 X L N (overpainted, SN 8000720)
1979 TE80 GS. Neck: 12=7 A, Body: 12=7 GS A (SN9005303)
1979 ST100 GS. Neck: 8=3&4 A, Body: 8=3=GS. (SN 9003909)
1979 TE80 GS. Neck: 12=7 A, Body: 12=7 GS A (SN 9005420)
1980 TE120R WR Neck: ?=15 A, Body: Not known (SN 0012035)
1980 ST80 GS. Neck: Not known, Body: 3=8 GS A (SN 0006409)
1980 ST100 N. Neck: 6=1 A, Body: 6=1 N A (SN 0000639)
1980 ST100R GS. Neck: 3=9 A, Body: 1=4 GS (SN 0000290)
1981 ST80R MR. Neck:Not known, Body: 4=1 MR A-X (SN 1013537)
1981 SS80 YS. Neck: Not known, Body:1=6 YS A Z (SN 1012478)
1981 ST85 MB. Neck: Not known, Body: 9=2 MB A
L:
1978 ST100 OW. Neck: 8000720, Body: ST100 X L N (overpainted, SN 8000720)
O:
1984 TST60 SP. Neck: Not known, Body: SP Y 6-5 O (SN 21920) Purple Sparkle
1984 TST60 SR. Neck: Not known, Body: SR Y 6-5 O Red Sparkle
W:
X:
1978 ST100 OW. Neck: 8000720, Body: ST100 X L N (overpainted, SN 8000720)
1980 ST60R FO. Neck: 1-1, Body 2-1 (struck through), 1-1 (handwritten) FO X. (SN 0016208)
1981 ST80R MR. Neck:Not known Body: 4=1 MR A-X. (SN 1013537)
1981 SS40 YS. Neck: Not known, Body: 5=5 YS X (SN 1102021, Nagano build)
1982 ST55 R GM. Neck: Not known, Body: 5=13 GM X. (SN L01762)
1983 ST50 FO. Neck: 7=1 NM, Body: 7=1 FO X (Block logo)
1983 ST55R. Neck: 5=12 MRH, Body: 5=12 MR X (Block logo)
1986 TTE55 BL. Neck: 7-12, Body: 7 12 BL X (SN 226824)
Y:
1981 ST70 YS Neck: 10=8, Body: 7=2 YSO Y
1982 SS65 N, Neck: Not known, Body: ?=25 N Y
1982 SS50 R MR. Neck: Not known, Body:8=17 MR Y. (SN 2024070)
1984 ST60 OW Neck: Not known, Body: 10=2 OW Y
1984 TST60 SP. Neck: Not known, Body: SP Y 6-5 O (SN 21920) Purple Sparkle
1984 TST60 SR. Neck: Not known, Body: SR Y 6-5 O Red Sparkle
Z:
1981 TE120 YS. Neck:Not known, Body: 10=10 YS Z
1981 SS60 OW. Neck: Not known, Body: ?=2 OW Z (SN 101479)
1981 SS80 YS. Neck: Body:1=6 YS A Z (SN 1012478)
1981 SS70S RR. Neck: Not known, Body: 1=2WN Z (SN 1023532)
1981 ST55 MG. Neck: Not known, Body: 1=3 MG Z
1981 ST65 MG. Neck: Not know, Body: 10=6 MG Z (SN 1020940)
1982 ? SS?? All black BB. Neck: Not known, Body: 4=8 BB Z
1982 SS 40 BB. Neck: 12=1, Body: 12=1 BB Z (SN 2026559)
1983 ST55 SO. Neck: 12=6, Body: 12=6 SO Z (Block logo)
1983 ST55 SO. Neck: Not known, Body: 6=7 SO Z (Block logo)
1984 ST55R OR. Neck: 7=3, Body: 8=2 OR=Z
1984 ST50/60 GS, Neck: Not known, Body:5=12 GS Z
Multiple letters:
1978 ST100 OW. Neck: 8000720, Body: ST100 X L N (overpainted, SN 8000720)
1981 ST80R MR. Neck:Not known, Body: 4=1 MR A-X. (SN 1013537)
1981 SS80 YS. Neck: Body:1=6 YS A Z
1983 ST55R. Neck: 5=12 MRH, Body: 5=12 MR X (Block logo)
1983 ST50 FO. Neck: 7=1 NM, Body: 7=1 FO X (Block logo)
1984 TST60 SP. Neck: Not known, Body: SP Y 6-5 O (SN 21920) Purple Sparkle
1984 TST60 SR. Neck: Not known, Body: SR Y 6-5 O Red Sparkle