I will post/link what I know about Weber date codes. I don't think they have much to do with gas go-anywhere, but it might help anyway.
1985 SL1 or SL2=Genesis XX,XXI,Jr with LP
SN1 or SN2=Genesis XX,XXI,Jr with Natural gas
L1=Genesis 1 LP N1=Genesis 1 NG
L3=Genesis 2 LP N3=Genesis 2 NG
L7=Genesis 3 LP N7=Genesis 3 NG
1988/89 L4=Genesis 4 LP N4=Genesis 4 NG
L5=Genesis 5 LP N5=Genesis 5 NG
1993 KL1=Genesis 1000 LP KN1=Genesis 1000 NG
KL2=Genesis 2000 LP KN2=Genesis 2000 NG
KL3=Genesis 3000 LP KN3=Genesis 3000 NG
KL4=Genesis 4000 LP KN4=Genesis 4000 NG
KL5=Genesis 5000 LP KN5=Genesis 5000 NG
PL5=Spirit 500 LP PN5=Spirit 500 NG
PL7=Spirit 700 LP PN7=Spirit 700 NG
1994 A U T H O R I Z E D (1994=EH; 2013=AT)
1 2 3 4 5 6 7 8 9 0