The regular JA2 (sold by Strategy First) is version 1.12 (normally reserved for the Gold Pack but eh). It's standalone, and doesn't include or require any other part of the series to run.
The JA2 Classic (sold by TopWare) is only available as a DLC for Wildfire and is version 1.03 (not even 1.07, which was the last pre-Gold build). And the base price is $2 higher.
And no, the version tag for the installers is not correct either - 6.08 was a version exclusive to the Russian release; the latest English one is 6.04 and the latest German one is 6.06.
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The rights to JA1, JA2 and their standalone expansions are notoriously a maze. TopWare got the rights to Wildfire in 2005 when i-Deal Games invoked
breach of contract with then-rightsholder of the IP, Strategy First, and sought someone else to publish a fixed version. The catch with vanilla JA2 is that the original boxed release of Wildfire also included JA2 alongside Wildfire, and that's probably why nobody bat an eye when JA2 Classic appeared on the S-store in 2017. And the reason how they have such an ancient build is that the original TopWare (the one that was closed in 2001, of which the current TopWare is the successor of) was the original German publisher of the game, and released it 3 months before the rest of the world got the game.