Nothing was reduced here. The BOP lists your estimated release date which includes good time that you have not lost.

You serve 85 percent of your sentence in the Feds if you don't lose goodtime. The numbers listed work out to 85% (there is a little bit of wonk in how they BOP calculates this number. It recently got changed as the BOP used math that reduced good time calculations and had to be told how to do math in the First Step act).

https://famm.org/wp-content/uploads/faq-federal-good-time-cr...

There have also been reductions via the First Step act but I don't know how that ended up. You got reductions for working at the Federal slave labor sweatshop (UNICOR) and for 'Programming' (taking their classes) but the BOP was fighting these pretty hard back when I was paying attention to these things a few years ago.