Standard scripts have always played a key role in the OMSI modding landscape. No matter what one is messing with, be it a ticket printer, a dashboard, an engine, or a bus stop's arrivals/departures display, chances are that at least a subset of the functionality of the object or subsystem was derived from the standard MAN SD/NL/NG and scenery object script base.
Question: What is it exactly, legally speaking, that grants us modders the right to modify and redistribute (portions of) standard scripts? Judging from both the script file headers and the OMSI/Aerosoft EULA, it appears that everything that "the product" (OMSI) comprises -- thus including the SDK and all standard content, in turn including scripts --, is copyrighted and unavailable for modification/redistribution without explicit consent. Obviously I must be missing something, for otherwise at least half of all the mods published over the past decade would have been deemed copyright-infringing, effectively precluding their publication, via the (quasi-)official channels at least. So is there somewhere an SDK-specific exception clause, that relaxes the normal modification/redistribution restrictions for non-commercial uses? Or is just silent, informal approval/"tolerance" by MR-Software (RIP) and/or Aerosoft what we have been witnessing all along? Or has everyone ever having modded/redistributed standard scripts gone through the trouble of seeking formal approval by the copyright holders? (of course the latter is not the case -- I'm just trying to make a point).
Context: I've always published my mods under copyleft licenses (e.g. Unlicense, CC0, WTFPL). But, when mods depend or derive from standard scripts, I've also felt compelled to weigh on the side of caution, by adding the restriction clause that "redistributed content is subject to the terms of its respective authors/owners". That clause annoys me and I'd like to get rid of it if/when possible, since it effectively cancels out my intent of dedicating mods to the public domain. That's why I'm asking this question -- to help shed some light on the legal background and ramifications, and make a better informed decision henceforth.