Hi All
In terms of Trainz, 'DLC' (Downloadable Content) refers to payware content available through our automatic download 'DLC' system. This is listed in the 'get new content' menu within Trainz, and is also available through Simulator Central.
As to how quickly new releases appear, for the most part the DLC packs are 3rd party packs. As such, they appear as quickly as the 3rd party creators can create and release them

The official DLC's aren't our main focus, although we have released a few to bring some new items to Trainz as well.
Keep in mind that we have been selling DLC's, either via the old 'exe' file system (or as cdp's for 3rd party content) or via our new DLC system, for approximately 5 years now (for TS2009+). In fact, we've also sold add-on packs (what are now known as DLC's

) for quite a long time as well, it's definitely not a new thing.
@Boyerm25
The routes being referred to at this stage are 3rd party routes. These are either routes that are too far from completion to be included with TANE, or routes that the creators wish to release as payware/DLC. Some may also be released for TS12 first as well, depending on when they're finished and which version the author wishes to release it for.
Regards