The glossy curves we have available are known good custom curves made for customers over the years, so there are some duplicates for the same paper, for different ink sets.
The "3800-3880-MPS-Type5" curve was made with the Selenium or Warm-Neutral inks, and "3880-WN-SEL-NU-JCStype5" curve was made for a customer using a custom ink set consisting of Warm-Neutral, Selenium and Neutral. Both are similar, and both should give you good results with your 3800/3880 on Type 5 paper. Custom curves are made for a customer's specific printer/ink/paper/computer setup, so provide the best output for their specific system, and others using a similar setup can use the curves to get good results with their system, though custom curves made for your specific setup will always provide the very best results for your setup. When we make custom curves, we open and check the resulting curve structure to others for that printer model to see if it's in line (and can be used by others), or has abnormalities due to the customer's setup (which may produce good results for their setup, but can't be used by others).
I have attached a screen shot showing the two referenced curves, so you can see how they compare. The MPS one has a slightly higher black ink limit, and the individual curve structures are ever so slightly different in areas, but overall the two curves are very close and good for other people to use with their 3800/3880 Piezography setups. Both are good, and one is not "better" than the other- use whichever you prefer.
Best regards and happy printing~ Dana