The Magic Bullet Looks is software that was added to Cinema 4D. Going back a few years is always problematic, as tools have been added to newer versions naturally.
Your question is general, meaning I would need to list a four-digit number of functions, tools, and objects in R19 already and what they were not in comparison to R25. Since those release number combinations can easily create over a hundred combinations, that would take a few days per pairing. That is not possible to provide here.
R19 was released in the Fall of 2017. If you can access R19, open the file, copy everything from the Object manager, open a new project, and copy things into it. Since you mentioned modeling only, timeline and render settings don't matter. Does it look OK?
As long as we talk about modeling, the safest way is to export the model in obj or fbx and share that with your client, they can send you the R19 file back, and you can check if they got everything OK.
One side note, this forum is for Site Issues only. Please remember this; thank you. I will move this post to the Q&A forum.