My experience with this developer shows that it loses steam at about 4 hours. It is still active but development times will need to be lengthened to compensate. That is based only on time in a tray...I don't have the number of sheets calculated since I haven't depleted it in that manner.
The addition of additional KBR will not extend life in this case.
This should be mixed immediately prior to use...once the chemicals are in combined state they will begin to oxidize. If one has accurate enough scales then the formula recipe can be cut in half for one liter of use solution.
If one wishes to mix stock solutions then this will need to be a multi part stock like the ABC formula. The developer agents and bromide in one part, the sulfite in the second part, and the carbonate in the third part. If I were to do this then I would calculate this out to arrive at the amounts of stock to add to arrive at use dilution. I haven't done that myself and thus have not made the calculations.
Sounds like something for me to work on.