Fiddled around a bit in Javascript/Vue. I now have a date converter in semi-working condition, courtesy of rlucine's Timeline Deduction & Date Conversion Algorithms. Most of what's important is written on that page, so I won't talk about it much here, but:

• When I say semi-working condition, I mean that most of the dates convert fairly well; same dates with different date formats MOSTLY map onto each other, and when they don't, it's just very slightly off by like, a cycle or so, which suggests precision errors.
• I...don't know if my calculations for post-Penrose cycle 3000 using Vineta cycles are correct LOL. I need to manually check this and I'm lazy.
• I don't know if my date difference calculations are correct. Rudimentary checks suggest they are? I'm honestly surprised, because historically (homework-wise) I have always had mysterious issues getting my results to align with expected values.
• The code can be viewed from the page source, but it's terribly ugly and difficult to read at the moment because I was just trying to get it to work and went from trying to use the pseudocode algorithms (which contain a few errors I think) to ripping out the C code (which I know should be working)...it's just a frankensteined mess. I'll need to clean it up I think.

I'm quite proud of getting it working, but I don't know if I want to post about this on social media because I'm a little leery of it spreading and becoming used as a public resource, especially with the mysterious precision errors. Sometimes you post a resource online, and then people use it as the source of truth (have had this happen with my translations in other fandoms) and I get scared that I made a mistake and now it's just ingrained in the fandom consciousness...

Thank you rlucine for gut-punching me several times with your post :) I am obsessed.