Trainz Classics is the term N3V Games used for its earliest release of Trainz technologies back in 2007. The concept was to get high quality content with well designed and developed routes from 'Auran Partners' on a regional theme, each with multiple well designed sessions for great playability. The first offering, 'Trainz Classics 1' or 'TC1' was not well received. Focused on passenger rail in the New York City area it was quickly judged as having too little content to be of great interest, so saw tepid sales at best.
Very shortly afterwards, less than two months later, N3V published TC2, or Trainz Classics 2, and it quickly became apparent the user community verdict was pretty much the same. Within a couple of months, the North American publisher (Paradox Interactive, Toronto) exercised its exclusive legal rights to publish a combined release, and it is that version TC1&2, as it is known, which saw much wider acceptance. Over half a year later, having learned their lesson on sufficiency of content, the British-themed release 'Trainz Classics 3' did a much better job of providing value and was better received by those interested in British Railways.
Both versions lacked the breadth and depth of assets found in TRS2004, and most Auran authored legacy assets are only now finding there way onto the Download Station; This is more a major shortcoming than it might appear, many assets rely on parts (kuids) based on Auran's basic traincars.
In a nutshell, the Trainz Classics were TRS2006 in a new skin with much less eclectic and wide ranging content as built-in assets—as these were limited to the dependencies needed by the few large routes. While there was less maps variety, the versions did showcase large involved maps modeled on long routes with a lot of Driver opportunities for varied kinds of Sessions, so was accepted by those much interested in driving Trainz. The internal technology level, was little improved from the Auran releases, excepting the Trainz data model schema for locomotives was overhauled in Trainz Classics 3 (TBV v2.8); that release begat today's enginespecs with little change except for a pair of tags boondoggle in the kind engine-sound data model during both TS09 and TS10 (TBV's v2.9–v3.3); those versions complain if given the tags data, yet the parameters were in Trainz 1.0—TC3, and again became mandatory in TS12.The modeling sub-community tended to stay with either TRS2006 or tried and true TRS2004 which gave them direct access to their raw files for adapting elements to other models. To this day, when 64-bit TANE is the current release version, many modelers stick with TRS2004 to manually manage their file structure, which is indexed by kuids and is uncommitted until the GUI's run. TRS2006's CMP preprocessed files and used a hash code that hid data from its very creators! Being able to 'borrow parts' when building something new is a big time saver creating from scratch, so who can fault them?