ELU 9.720-9.990 was confirmed as an insert range because notes were (presumably) found inserted and replacing regular notes. The size of the range corresponds to a ream of notes, and the number of sheets in the ream is equal to the skip interval on each sheet. So for ELU 9.720-9.990, that's 6000 sheets. Finding a handful of inserts from this range does not prove that all 6000 sheets were used as inserts. In fact, when the printers cut up sheets, it is 100 at a time. We know this from patterns of cup marks through every 100 note bundle.
The elephant in the room is the fact that not every note from an insert range is a true insert note. That's a fact that no insert collector or brick hunter wants to hear because it is a threat to the viability of collecting inserts. That this has been happening even as far back as asterisk and X notes is proven, and yet the essential truth of what is happening is largely ignored, deliberately or otherwise. Many people don't want to accept that inserts and regular notes are printed the same way. The only difference is the order in which notes are issued. It's akin to taking two stacks of sheets and mixing them together like playing cards.
So what is happening is the printers are grabbing a few sheets, using them as inserts in reams of regular notes, and then cutting up the leftovers and making them into bricks just like they are regular notes. I seriously doubt they are keeping track of the serial numbers of replacement sheets because each sheet represents 45 smaller ranges. Anyone who thinks there's a "master list" of inserts is just fooling themselves.
I agree with the comments of abyss that pricing based on population is what matters most. This is why smaller ranges tend to cost more, but for every range, there exists the possibility that at least a portion of the notes are not true inserts. Collectors and time will determine what the value of these notes will be. But if the information is being incorporated selectively into the catalogue, and there is conflicting information about insert ranges between the catalogue, Gilles' lists and the SNDB, then I think collectors are being done a huge disservice.
