There's something cool about being known for doing a certain thing well. One of the benefits is that people come to you wanting to give you money to do that thing for them. Most of the time the request is fairly general: "I like how you painted those guys. Make them kinda like that - but, you know, just make it cool." But when it comes to my Doom miniatures clients they are a lot more exacting.
When I painted my first set the client had very specific requests in terms of colors. It was mostly geared towards making the colors of the minis closely resemble the colors on the sprites from the original video game(s). That client was very happy with the results and the resulting photos seem to have traveled far and wide to such a point that I will have painted five or more sets of the minis by the end of the year. The interesting things is that the subsequent clients have all wanted me to duplicate the work that I did for my first client.
In itself, this isn't really a problem. Since I have good photo reference it shouldn't be a problem to do what I did before. The fact that I made some videos on the topic make it a little easier since I have that reference. But other than the videos I don't really have any notes. My painting can be fairly spontaneous. Luckily, I tend to focus on certain colors over other colors and with the reference I can generally figure it out. When I can't, well, things don't always reproduce exactly as before.
The other problem with trying to duplicate my previous work is that I am rarely satisfied with my previous results. If I'm just doing what I did before then I feel like I'm not moving forward with my painting. Who wants to make the same mistakes over and over on purpose? Unfortunately, when you're asked to reproduce a previous work this is probably what you're going to have to do.
At this point I try to make adjustments where possible and hope that the clients will see it as improvements. If not... it's back to the old recipe.