Need help, age of GE furnace

Need some help determining the age of this GE furnace Sr # 580194. My chart says the last 3 digits are the age. 1 being the year and 94 the week of manufacture. As you can see this does not make sense. Home was built in 1981. Did I read the #s wrong? Could it be the original?

Serial looks like 34 to me…

if it is XX134 its 1981

GE went away and was acquired by Trane in the Mid 80s

Thanks, 34 makes sense.

Looked at it from my iPhone and zoomed in…