When hovering over the production/science/culture UI elements that tell you how long something will take, I'm seeing some numbers that seem to indicate how much more output I need to reduce wait times. Right now my Inca game has 516

/ 570

on my next policy, with 4 turns left at +15

per turn, and then when I hover over that, it shows "3 turns -9
4 turns +6

". I get that these are supposed to give you some idea of how far you need to go to speed up things, but I don't get why there are two separate turn counters with +/-

values next to them. Can someone explain precisely how to read these numbers? And shouldn't the "3 turns" have a
positive culture number next to it to say how much more culture per turn I need?
Also, when I hover over luxury resources and the yields menu comes up showing tech and improvement bonuses and whatnot, there's this one bullet point that says "+1

Gold for all nearby luxuries". As far as I can tell it doesn't actually seem to be doing anything for my gold per turn. Is it a leftover UI component from some mechanic that got patched out?