Amperex 6SN7GTB

does this indicate different manufacturing eras?

Yes. To change the tooling usually was a pretty big deal. So its not like one tube could have been made a few days from the other one. It would have taken some time to change the tooling (which is not cheap) on the line.

Yeah…I'll maybe send a note to those guys and they may know what's what. 

Try emailing Tubemonger and/or Brent Jesse with pics.  They might have some insight.

I have a pair that came with a Dennis Had "Inspire Fire Bottle" amp that have a side getter, and then I bought a back-up NOS tube with top getter and clearly a different design, although both tubes seem to work similarly and but clearly from some vintage I can't recognize (and why would I?)…no big deal, just curious. Both tubes are Amperex "Globe" versions with one having the Amperex printing and logo on the glass, the other (side getter from Had) on the base. Both also have the tube number and "made in USA" on the glass. Thanks!

The only Amperex 6SN7GTBs that I’ve seen, had bottom getters(on one side/from Europe). Apparently, there are other iterations out there though, per these pics. No info though(sorry): https://www.google.com/search?q=amperex+6sn7gtb&tbm=isch&tbo=u&source=univ&sa=X&...: