When comparing replenishing paper developers compared to film developers there are other factors to consider.
While film emulsions have a higher silver content per square metre, they are not developed to achieve D max. With MQ film developers the limiting factor with replenishment is Bromide build which begins to inhibit Metol activity as levels rise. To overcome this bleed replenishment has too be used, a volume of working solution is removed and replaced with replenisher.
In the 1950s Ilford realised switching from Metol to Phenidone overcame the Bromide build up issue. They worked on a PQ version of ID-11/D76 accurately measuring the actual depletion of the developer components with use, and were able to formulate a replenisher for top-up use. The developer was released as Autophen in the late 1950s. it was used for large scale photofinishing film processing machines. Unlike OD-11/D76 it did not collapse anfer many months of use, and just kept going. There's a series of 1950's BLP Almanac articles on the evolution of Autophen.
With paper developers development is to achieve Dmax, not to completion as some write. The capacity per litre depends on two factors choice of developer type, and paper base.
As with film developers thelimiting factor with developers llike Dekto/D72, D163, is being MQ developers their capacity is limited by Bromide build up, and the developer suddenly collapses.. Switching to a similar PQ developer very subtantially improves capacity at 3 or 4x.
Ilford's main paper developer used to be ID-20, an MQ formula, in the late 1950s this was replaced by ID-20PQ, identical excect the Metol was replaced by Phenidone. There were compalains that with the greater capacity as Bromide built up image colour was shifting warmer. Ilford refirmulated ID-20PQ as ID-62 halving the Bromide and adding Benzotriazole, which inhibits the colour shift.
ID-62 was never sold commercially, instead it was reformulated as a liquid concentrate, PQ Unuversal. The Sodium Carbonate was replaced by Potassium Carbonate and a small volume of Sodium Hydroxide to overcome solubility issues with the concentrate.
Ilford give the capacity of PQ Universal as 70 10x8 RC prints per litre, and FP prints 45, the difference is mostly the absorption of developer in the FB base. They also say a working tray life of approx 24 hours.
I use ID-78 a warmtone developer (once sold in powder form), essentially a variant of ID-62, a slight increase in Bromide and Carbonate, I mix as a concentrate (it was sold as Harman Warmtone developer). Typically I mix 1.5 litres of working solution, and process around 30 16"x12" FB prints in a session, which is close to PQ Universal capacity. The volume of developer left will have dropped quite noticeably.
As
@Camerashy says a couple of days in a Nova tank sounds about right.
Ilford used to make and sell Phenprint, and a replenisher, this was designed like Autophen, for a long life in roller transport paper process machines. I'm not sure how it differed from PQ Universal to improve it's working life and counter oxidation, it might be increase Sodium Sulphite. Ilford 2000RT Developer is the current equivalent but comes with hazard warnings.
Ian