Hm. You might say I'm a special case, because I have an explicit letter of permission (in a bank vault), signed by the TSR Vice President & Publisher of Record, formally allowing me to recover items from the trash and resell them, as long as they don't go to shelves in game stores.
(I thus have a substantial library of manuscripts used in product preparation.)
That said, hm, general employee snarfing... okay, imnsho only (remember, legal advice is worth what you pay for it):
First and foremost would be any actual or implied conditions of employment. Read the fine print. Second and close runner-up would be the company's Employee Manual and/or written policies regarding such interim materials.
That said, next up is whether the company still exists, and if not, whether its assets were sold or assigned to any third parties or other company.
If after those 3 stiff hurdles everything still seems okay, then:
1. It would appear so.
2. See above, but no, given clear skies in the above historical documentation.
3. Only if you have something in writing giving you explicit rights.
4. The author/submitter has no claim on any production materials.
5. Doubtful, unless they're of notable value AND something in the research (above) indicates a dispute in ownership.
6. Depends on who and what, but not, in most cases.
One notable landmark affects this class of items. The best such, Category A, applies to manuscripts prepared and/or published before the spread of computerized word processing are rarer than file printouts, and will see a corresponding rise in value in the future. Such hand-made manuscripts by notable authors in ANY field will skyrocket. Category B is thus printouts with extensive hand-writing and such, usually editorial. Cat C would be simple printouts of various pre-publication stages, and Cat D would be the files themselves.
That help?
Frank M (apparently one of multiple Franks hereabouts)