I worked with a gigantic research lab as an undergrad intern for a couple of months and the preprint of the paper summing up the results of the project I helped them with was recently posted on BioRxiv. My name does not appear among the co-authors and I'm wondering whether I should contact my direct supervisor, who is the project leader and the first author, and ask for co-authorship. I did read this question and the answers, but there is a fundamental difference in my case: my work was intermediate-step analysis, not final results.
I'm going to detail my role in the project in the following paragraph, and I appreciate any comments on whether this is something that'd grant me a co-authorship and worth asking for it. Briefly, my role was to do some intermediate-step data analysis in the initial phase of data analysis of the project: A data analysis that was used to do more helpful data analysis in the following steps, but wasn't a significant result from the project on its own.
The field is Comp Bio - molecular bio - bioinformatics and the papers resulting from this type of project often have an endless list of co-authors. The project took 5-6 years, but that's not at all unusual for the lab, as they often involve a long phase of wet-lab experiments and data collection, a phase of data analysis (sometimes accompanied by supplementary wet-lab experiments), possibly ending with a short phase of interpretation and theory work (Physics, Computer Science, etc.). When I applied to join the group as an intern, they'd just finished the data-collection phase, and they took me in to help my supervisor with data analysis. That was the initial phase of data analysis, so they were just getting to know the data and my supervisor would usually ask me to clean up the data, find some macro-level statistics, create some plots, and they would use those in the lab meetings to find out what could be interesting to look at and what kind of analysis could lead to a story that could make the paper "Nature-worthy". None of my plots ended up in the paper, but one or two plots are very close variations of the plots I made (say a bar plot with 6 bars showing a certain measure of 6 samples, 3 of them are also in the plots I made, 3 of them were samples they were still deciding whether they want to look into or not when I was there), and one or two are the measure I made the plot for, but they added additional parts to it. There was also some data analysis that was redone after I did it, as they decided to repeat a part of the wet-lab to collect more data and increase the accuracy. Note that the preprint was posted on BioRxiv almost two years after I left the group (so there was still a significant amount of work, mostly data analysis and interpretation, done after me).
What makes me think I may deserve a co-authorship is that, although my supervisor could have done what I did during my time there more than twice as fast, I did spend a significant amount of time and energy and saved them half as much, and there was very little technical education there for me (the education was more conceptual in data analysis and research conduct) as my technical knowledge and skills would already exceed what was necessary for that work. In addition, what I did was what they'd have to do anyways to get to know their data and learn what would be interesting to look into, so I hope it wasn't useless. On the other hand, what makes me doubt if I do deserve a co-authorship, besides the relatively short amount of time I was a part of the project, was that they paid me as a full-time intern, and my data analysis was not my intellectual contribution, rather a technical work that I'd do upon the instruction of my supervisor (my supervisor would ask me to create a plot showing X, and I'd do so). Moreover, as far as I got to know the group, they're very nice people in a lab with an excellent name recognition in the field and I'd be very surprised if they would do anything unethical of this kind (especially because adding an extra name to one of those 50-60 co-authors wouldn't even cost a penny I guess).