I saw that there is a closed thread about this, and I thought I would toss in some added info. Sorry about the similar thread.
This is in regards to the Old Weller Original 107 375ml bottles that have an "84" embossed on the bottle.
I found a shop here in Dallas that still has several of these 375ml bottles. I bought one so I could examine it closer.
If you shine the back of the bottle against the light, there is a stamped serial number similar to the ones seen on Van Winkle products. Here is the one on mine:
13090807:16 (note: the "1" could be an "I")
If I read this correctly, it was bottled in 2008 at 7:16am. It fits the correct year just before they did away with the old looking label in 2009.
Also, the sticker has the "No" line in the top-left corner, but it hasn't been filled in.
Here is my hypothesis: They (BT) found a bunch of bottles from 1984 and decided to use them to save money and didn't figure anyone would notice. I have to admit the bottle shape looks old.