The first group are the giants of history upon whose shoulders newer versions of today stand.Trainz in all versions was supported by N3V Games until the adoption and announcement of the Trainz Life Cycle policy in 2010.
Note: Due to the catastrophic loss of the Auran Forum's servers and consequent imposition of a five week hiatus in that service during 2006, back checking and footnoting release announcements and code builds in this data has been sidestepped.
Auran and N3V Games have not been able to restore those lost years of forum posts, and we've better things to do with our time than chase references with only academic interest.
This aspect of Trainz is further complicated by Trainz nature, it is at the heart, a data base manager and a huge data base (the greater size in files) with satellite tools programs (especially for example, the GUI run time modules Surveyor, Driver, Railyard, and some others behind the scenes like Trainz Utils.exe) each of which may need patched or replaced with a service pack release or Hot fix.
Further, and the most problematic part as it takes some time when a user has a lot of downloaded content, a new update may also scan each item in the database, and where necessary, patch those to compliance with the 'new technology level' being introduced by the patch and corresponding to a new asset build tag number.
V2.5 and up Launcher Screens look prettier since TRS2006 and all its spin-offs like the TC's, and TRS2009–TS2012's, but since they use the same layouts for the same buttons all look pretty much the same. Hotfixes for bugs and adjustments of several things, not usually to make the whole work, but instead to make the whole work better after an interval of additional testing and while the programmer's are fixing one or more other minor bugs or adding an extended feature.