To do what you describe would require 2 instances of the game core, one to fix bugs on and the other add 'new era' code to.. Which would leave the new era code being developed on a buggy core!! Which in turn would lead to more bugs..
Another alternative would be to fix the bugs then add the 'new era' code. The preferred method.
Alternatively they could ignore the bugs and just continue with the 'new era' bugs, because, they will be bugs..
The fact the QA team If there is one, and past history shows there is not, is immaterial. Typically, code is developed, peer tested, game tested, user tested, then acceptance tested, and the quality assured.
Previous releases would indicate they go straight from dev to beta testing, ignore feedback and then release.
My bet is the QA team is smaller than the postal team. In fact they might be the same teams!