Hey hey! So unfortunately, there's a known issue with our recency boosts where the boost decay falls off too quickly. Essentially, the boost you added works, but it only significantly boosts dates within say, the last 2 days or so, and does not boost dates farther away (e.g. a week or more). So I'd definitely expect the results you're seeing, which is dates as far away as a year or more 
Apologies for that - it's definitely on our radar to work on ways to tune results more, although I don't know if the recency boost is on our short-term roadmap (I think we actually removed it from our documentation because it wasn't working as expected).
Here's a couple workarounds you could try in the meanwhile:
- Add the ability to sort by date, and highlight that in your UX
- Weighting by a specific year cut-off - for example, if you want to boost docs more recent than 2 years ago, you could add a value boost for the sub-2 year docs
Hope that helps, and let me know if the value boost workaround doesn't make sense and I can try to clarify!