I have donated to a number of charity groups through the years, railroad and non railroad. Seven years ago I donated a small amount to one of the large national research groups. I wrote my middle initial wrong just to see what would happen. I got a thank you with another beg letter from the first group. This group still sends me beg letters every few months and there are five ... yes, five other non-profit groups that send beg letters to me with the wrong middle initial. This proves that many groups sell your information to other groups which I do not care for. I have never sent the original group another penny because of their selling my information.
Most railroad museum/preservation groups are better. Among the best are the FEBT and the WW&F. They tell you right up front that they don't share your information with other groups and they send thank-you letters and sometimes small gifts depending on the amount of the donation. The best approach is for preservation groups to explain what the funds will be used for and in some cases such as the WW&F, there is a schedule of fund distribution so you know what projects you are helping. That's railway preservation done right.