Just hatched a Larvitar from a post event start 10K
So I guess they can be in either egg. I didn't expect that.
34 candies.
Answers
"Post event start"
Nope. Cleaned out at 4:00 and did not collect eggs until I got off work at 5:30 est...1:30 after the event start. I posted here at the time that I picked up a 10K egg after the event started.
Since I posted this i went to the Silph Road and it appears I'm not the only one. Also, Dratini are in 10K eggs but it appeared only in 10K eggs. Porygon seems to have moved to 10Ks exclusively.
"post event start" would mean "after the event started." Did you mean you got a larvitar from an egg that you obtained pre event start?
I had 9 2k eggs before the event started. All were typical. The events I got after the event started have given me an Aerodactyl, A wobuffet, and a few other cool things that don't belong in 2ks. But all my pre-event eggs were typical.