All I can say this one is made in 1998. I can't make heads and tail on the rest of numbers

Ah... Never paid attention to that numbers. It's possible that this ballast was made in 1998.

Vince; there should be a two-letter date code engraved on the backside. Mine is marked "YJ" and came out of a Genlyte-Thomas wrap light that i got at the ReStore. Mine says Valmont Electric Co. where your's says POWERLighting thought. I'm not sure how long Genlyte-Thomas has been around though so it may be pretty old and i don't know it... My grandpa's autobody shop's office has F40T12/RX troffers that look pretty old and have VAL-MISER ballasts in them.

I have a single lamp Val-Miser-Power Lighting ballast that has a numerical date code on one of the flanges. Anyway mine says 9808 which I guess is August 1998.

I think Valmont Electric bought GE's ballast division sometime in the late 80s and then sold off them to Power Lighting sometime in the 90s.

Oh so my VAL-MISER Valmont Electric ballast may actually be older than my Advance ballast. The Advance is from May 1997, a full year older than I am.