The Improved Military Production tech for Mongols has some inconsistencies, and I don’t know if this is one of multiple bugs. When doing the improved tech in two steps first normal tech then the improvement, some units gets extra benefits (according to the tooltip above what is intended, but according to time measurement it seems the other way around that doing the whole tech in one go gives less benefits than intended, this needs more verification as I was lazy to do extensive time measurements)
The following table shows the base production duration as well as the theoretical duration after getting the improved military production tech. In addition I show what the game tooltip shows in two scenarios: 1) the improved tech is research in one step. 2) the improved tech is researched in two step.
I used to think that the game always rounds durations down (based on the tooltip) but I decided to measure the actual production time for some cases with discrepencies e.g I measured the production time for 10 Lancers in both scenarios, measurement error for the initial and final time is quite small + it is diluted over 10 units therefore it can’t explain the difference of 10s in producing 10 Lancers. For the scenario in which the tooltip shows 22 (1 step) I actually measured 23s per Lancer and for the case in which the tooltip shows 21 (2 steps) I measured 22 seconds per lancer.
The following two screenshots show the two different durations of the tooltip.
Lastly, it is worth mentioning that the tooltip for this tech is a bit awkward, the normal version speaks of production speed while the improved one speaks of duration reduction, while they are equivalent this can be confusing.
Edit: I forgot to mention that I suspected a “double rounding issue” when doing the tech in two steps, but I found it not to be the case.