I’m a little confused here, and I’m not an NLP user yet, do you mean that you batch convert a random selection of colour negatives from different film stocks? I thought that batch processing was designed for images from the same film, or several films together using the same film stock and so having the same film base colour and density.
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With such huge quantities, I really don’t have time to try and figure out the different film stocks, I scan more than 1,000 negatives a day. But the images all come from one project, one photographer so it’s mostly the same film stock across the whole thing.
edit: Also I’m absolutely not an expert about NLP, far from it so don’t take my way of using it as a guide! The people who helped me in this thread seem a lot more reliable 
To be honest, and I don’t want to sound like I know for sure, but just based on my programming and scanning experience, if we are talking about hundreds of thousands of negatives I would seek to develop more automated pipeline. There are scripts out there which can run conversion from command line which means they can be fully automated and handle thousands of images unattended. Here is the sample of Python script I wrote a year ago (you don’t need to know Python to use it) that works quite effectively, available here for free : GitHub - vsaddr-github/neg2pos: Converting negative image into positive image and very short demo video is available here: https://youtu.be/vczMHo_2wiM . I would think that with that volume the inversion, quality and size of resulting images are negotiable. So there is also old Negfix script, no longer supported, but it works, I played with it and it gave me decent results. The other option is talking to authors of NLP, Grain2pixel or Negmaster and contract them to make custom scripts. My guess that whoever is ordering the scanning job is in race against time, so few bucks custom scripts may cost is money well spent. Just my 2 cents
Thank you for the suggestions, I was not aware of such solutions.
I’ve been doing things manually (except for the batch-conversion part) by myself until now and I’m already pretty far in the project so I think I’ll stick with my routine for now but in the future if something similar happens, I’ll definitely consider more automated options!
If they’re mostly the same film stock then that makes a difference, sorting them so they are the same for each batch ought to help I would have thought, some film bases can be very different. Still, I’m not an NLP user as I say. Thanks for that.
Look at my latest post: NLP v3.1 Beta Issues Thread - #7 by Digitizer