how OLD is my bottle?

[TopCat]

I have 2 full, unopened bottles of Old Fitzgerald 6yr old Prime that I wonder how old they are...both have 200ml (6.8 FL OZ) marking in the manufacture of the bottle towards the bottom, on the back. Says "liquor bottle" on very bottom and tax stamps are intact. The tax stamps are "052251426" and "086740102" but I can't make out the state, so I doubt the year is contained in the numbers? There is some light numbers on the very bottom, again in the manufacture of the bottle but it is hard to make them out as well. I'm guessing these are 1970's? I assume they are still good to drink?! Thanks,

[bourbonv]

If they have both Metric and Fluid Ounce measurements, it places them in the transition years of 1979-1981.