Hi Tony,
Commercially, that really isn't the point though is it? If Microsoft took this approach, that it is sufficient that a pristine user configuration updates pristinely, most of our PCs would not survive a Windows Update.
By definition, an SP's purpose in life is naturally to encounter user pre-existing, "off-pristine" conditions. The SP should be more "sailor-proof" and fix pre-existing conditions before imposing the changes, if thats whats need to get a successful result with a good majority of users. For example, why not run a rigorous database review, with interaction with the DLC/DLS database, before the changes are applied?
Please take KotangaGirl's Post #233 seriously, she's hit the "commercial" nail on the head. None of us want to see users permanently frustrated away from Trainz due to SP update problems. But this is what will result if the design objective of the SP is not improved (i.e. account for pre-existing problems such that it leaves things better off than before) . Not all user SP1 issues are neatly summarized in this thread, many users have started their own threads for SP1: taken all of these in sum total, I dare say you have a commercial quality problem to fix.
Trainz has come a very long way technologically in 20 years, and it would be a grave travesty that it cannot make traction or lose followers for something as simple as proper DLC update.