You can tell if it's a double baffle because there's a strip of wood going horizontally across the front of the speaker. There is the baffle the speaker is mounted to, and it's got 4 pieces of wood in the corners that space the second baffle out a little. From what I gather, the second baffle helps to mute highs and mids a little and makes it have a more bottomy response. Works for me. It's the only 15" cab I've ever really liked. But I haven't tried the 70's Thiele cabs like you have. I may pick one up if it's cheap enough.
Here's a pic of mine disassembled and ready to ship to Jess. It has the front baffle turned around so you can see it:
Here's a pic of mine disassembled and ready to ship to Jess. It has the front baffle turned around so you can see it:


