I've been doing some 1974/1998 database work this week!
Came across this response/explanation from Riz (from the SI EHM Forums) from earlier today, where he talks about some of the "under the hood" work that's been done with EHM:EA that eventually should allow for improved retro databases (i.e.
eventually, in the future/once there's an editor, the potential to correct league rules, league structure, playoff format, and more!)...anyways, in response to questions about adding Leagues, here's what Riz said
In the 2007 game, all the leagues were hardcoded, meaning the way each league worked was actually coded on a league-by-league basis. That meant the game could only support that one hardcoded set of rules for each league and any changes to league structures/rules had to be changed in code. So even if you created historical databases with historical start date and team/player data, you were still stuck with all the leagues running exactly like they were coded to run without the ability to change that.
As you may have noticed, the new game has done away with all the hardcoded leagues and instead all the leagues are implemented in the database itself as sets of rules on how to setup and run the league. This allows different databases to have the same leagues playable but with different structures/rules. For example, check the historical 2006 default database for how differently the leagues work compared to the default 2014 database and its playable leagues. The importer currently adds these rules into the new format database based on what rule set you have defined in the import config (2006 or 2014 sets are currently supported). I'm sure that once people understand what a major leap forward the new system is (and what doors it opens for future expansion of the game) they can really appreciate it.
So no, it is not currently possible to just lift the old rules from the old code as pretty much everything relating to the leagues and how they are run in the game has been re-written. What I am doing is converting the old hardcoded leagues and their rules/structures into the new database driven formats and obviously for some leagues it takes more time. But the upside is that most of the leagues do actually share a lot of the rules and structures with other leagues, so once those rules have been implemented in the new gamecode, those kinds of leagues are fairly easy to add as playable leagues (for example the leagues in the last update).
As I posted in the thread
http://community.sigames.com/showthread ... 459-Update I'm really excited about the potential for improved retro databases! 
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but hopefully...eventually...someday 
