Varactor Diode Specifications

I have a design that uses a varactor diode in a tuning circuit. I came across a paramter called the "rank" under the classification section of some datasheets.

This has something to do with the tuning and capacitance ranges. I am not sure what it means. I would appreciate some help. I have attached two datasheets for reference. Thanks.

Looking at the 1471, it seems they can guarantee a min/max delta of 3pF, but they can't hold the average value any better than +/-3%. This would make it easier to design a circuit that depends on capacitor ratios. Otherwise the min/max of 30/40pF might be excessive.

I'm a still a bit confused. I have used varactors before in quick and dirty CMOS VCO circuits, but never came up on this spec before. It didnt really matter then because I didn't need to hold a tight frequency.

It seems that I would have to actually measure these parts after I buy them or special-order them from the manufacturer with a screening option in order to guarantee that I have the correct part if the design calls for a particular part rank for optimum performance. Perphaps these are not standard OTS parts. Might be a clue as to why Digikey does not stock them. Oddly enough, I have only seen this spec with Japanese manufacturers.

Could you also expand on the "design with capacitance ratio' statement? Thanks.