Here's a database I put together from information gleened thru the manuals and various articles written about Simplex over the years. As we have all gotten to know, there are very few hard & fast rules as to what parts were correct for any particular year of bike. The running changes at the factory, the ups & downs of their fortunes while Paul Treen was in business all play into the great variability of what parts might be on what bike. Added to this are the many variations to title & registrations used by the different states back in those days (to some, it was more important what year you were registering rather than what year the bike was made).
Please let me know about other variations or corrections. I'm sure the list will continue to grow and change, but at least this gives everyone a base to start from when trying to decide what year their bike was made (the frame & motor changes will help those with bikes built prior to frame numbers).
Mike Sal