I'm not entirely sure. This account dates back to 2009 and has an LJ-generated free style which I haven't messed around with at all because I'm a writer, not a designer. When I go to "home" and then to "Edit Journal Style" and scroll down to "2. Select a New Theme," I see this option:
The menu option "Switch to Old Style system (s1) is circled in red in the lower left corner of the image. When I clicked that, I get taken to a warning screen that asks me "Are you sure?" then states "The S1 style system is no longer supported. We recommend that you stay with S2 for the latest features and themes." There is a green button underneath that says "Keep me in S2" and a grey button that says "Switch me to S1 anyway". I've pressed neither, so I have to assume that I'm in S2 right now.
tl;dr - As someone who is not a designer or a programmer and does not know what diferrentiates s1 from s2 I believe that anyone who created their journal at least as early as January 23, 2009 - has a default s2 style. But as I said: I'm far from an authority here.
no subject
The menu option "Switch to Old Style system (s1) is circled in red in the lower left corner of the image. When I clicked that, I get taken to a warning screen that asks me "Are you sure?" then states "The S1 style system is no longer supported. We recommend that you stay with S2 for the latest features and themes." There is a green button underneath that says "Keep me in S2" and a grey button that says "Switch me to S1 anyway". I've pressed neither, so I have to assume that I'm in S2 right now.
tl;dr - As someone who is not a designer or a programmer and does not know what diferrentiates s1 from s2 I believe that anyone who created their journal at least as early as January 23, 2009 - has a default s2 style. But as I said: I'm far from an authority here.