I taught professional photography for 32 years, and I used to write books and handouts for students. I'll be using some of the "older" material, and start adding new material as I progress.
You're all invited to visit, and as always (although I haven't heard yet from anyone), you're invited to provide me with corrections, feedback, or even to suggest articles that might interest you (if I can do that).
Looking to see if there is a screw holding a cast iron toy together to determine if the toy is an original or a reproduction is good clue, but it is not absolute. I can think of two manufacturers that routinely used screws in the assembly of their toys. That would be Welker & Crosby, and Dent. If it is a Phillips head screw, then is is definately a reproduction (unless someone replaced the screw). Phillips head screws were not invented until the early 1930s.
* I'd like to thank John for helping me correct what I had written. It's always great to have someone more knowledgeable that I, to lend a hand.