A good question, Allen. I realize this is a bit off-topic, and it is difficult to provide an answer that would suit all possible situations, but here is an overview from my personal perspective:
Authors who are requesting assistance from others should do so with a personal letter that is polite and gets right to the point. First impressions are very important. A letter is always the preferred way to establish first contact. E-mail is usually OK too, but has the disadvantage that many people and companies get hundreds of e-mails a day, and a lot of people just use e-mail as a means to dump things from their desk onto somebody else's desk, so it is easy for your communication to get misplaced. Writing a letter at least demonstrates that the matter is important enough that you were willing to devote some effort to it!
Telephone is usually the worst way to establish first contact. Bothering people who do not know you with phone calls is likely to guarantee you don't get any help. Try writing a letter instead and leave it to the other person to suggest whether they want to talk by phone.
You are most likely to get help from others if your questions are very specific and include the entire scope on the first asking.
Respect their time as being at least as valuable as your own, and do not waste it. If you have to mention a "deadline" in your initial request, you did not plan ahead adequately. Don't be surprised if you don't get any response!
Never ask another author to hand over his list of contacts, it is both lazy and a sure way to make yourself unwelcome! You cannot reasonably expect somebody to jeapordize their access to information for their own projects, in order to make your task simple and easy.
Don't expect others to do projects of enormous scope that you are also capable of doing, unless you are going to credit them as a co-author. If the task requested is going to involve "writing a book", the person doing the task might as well be the "author"!
In general, people who work in the railroad industry usually do not appreciate it when authors try to drag them into situations that involve making them a "go between" to pry information out of their employers, or volunteering information on their friends and contacts in the industry. Some of these situations may be just an inadvertant mistake on the part of the authors, who do not realize the consequences of what they are requesting.
I have noticed that some authors are quite oblivious to the passage of time. I have had writers ask how they can get in touch with people who worked on the development of locomotive models produced in the 1940s, not realizing that anybody who was a manager at a locomotive builder in that era would be at least in their late 80s now, if not a lot older. The best time to interview them was many decades ago!
There are some new roadblocks to writing which have developed in recent years. Some inexperienced writers are unaware that the legal environment in the US has resulted in many large companies putting specific time limits on the retention of documents, due to the risk of enormous "discovery" file searches in the event of a future lawsuit. The consequence is that authors seeking specific details such as sales records may have a very tough time finding answers, and need to keep this in mind when they are seeking information. Some things may now be very difficult (or even impossible) to research no matter who you ask. We are fortunate that there were a number of dedicated authors in this hobby who did a lot of research in these subject areas back in the 1970s and 1980s, when the manufacturers were much more receptive to such questions.
Inept handling of communication by authors and writers is by no means limited to the younger or even the less experienced people in the hobby, there are a few very experienced authors out there who have the same problem.
Now back to the BL-2.