Habarudo said:
Yes.
If the person who did the LO also does the ganga, its just called "genga".
If someone else does the genga, its called 2 Genga (第2原画). 2nd KA are credited by studios at time too (which is unfortunate).
Anihunter said:
Varies, some shows do it because of the industry's production woes, others just do it to make sure there's a base standard to work off of. How many animators/studios are credited for it also varies between both series and individual episodes.

Technically speaking, 2nd Key Animation has been a thing since the 60s, it's just gotten more common since the mid-2000s.
Thank You!