OK, so I was trying to figure out some more timeline information. I think, going with keeping our current storyline and all, I have it worked out. In my New Worlds app I have Kali at 25 (which actually works perfectly with the girls original birth year and upgrading them to 2012), so I went with that being how old the girls are. I have that Liz left not long after her 22 bday, which means Markus left not long after Kali's 23rd.. so 2009 for Liz, 2010 for Markus? Which means Dec 2010 was also when Dark Water replaced them..
Like I said, I think I got it right looking through all the information we'd had for new worlds, but lemme know if you disagree!