running through black toner very quickly, Supply Status page seems wrong

[Magpie54]

Ordinarily, when I put a new black cartridge into out Laserjet CP4025, the Supply Status page says that the cartridge can supply about 8500 pages and we'll get a Low Cartridge message when there are about 1000 pages left. Lately, when I put a new cartridge in, the Supplies Status page says that the cartridge can supply about 4000 pages and we get a Low Cartridge message at about 500 pages. The other cartridges are behaving normally. We only use new HP cartridges. I've also had to replace the toner collection bottle more frequently - much more frequently - than I have in the past.

I don't think we're printing any more than we usually do, and even if we were, it certainly wouldn't be enough to drop the pages supplied from 8500 to 4000.

Any ideas about what may be going on? Buying twice as much black toner is going to be a very expensive solution for us.

Thanks very much for your help.

UPDATE
I've talked at length with an HP repair guy, and they both say that their best guess is that there is something wrong with the cartridges, perhaps with the chips on the cartridges. Our vendor is an official HP Partner, (gold, whatever that means) and the dates on the box are relatively recent. Unless our vendor is doing something  shady, I'm at a loss.

[Repairatrooper]

Is it only the black that you have seen the page count decrease in? Is your firmware up to date? Do you print a lot of narrow media like envelopes? Are your print jobs mostly single page or multiple pages? Single page documents will cause faster wear. Keep in mind that the rating is based on 5% coverage and if you are printing more dense pages than than it will affect the page yield, sometimes dramatically.

[Magpie54]

Based on the Supplies Status page, it's the just the black cartridge. The others are reporting that they' re supplying the usual number of pages.   I don't know about the firmware but will check.

This is the main printer for a community college performing arts department, and we print a mixture of color fliers and double-sided text pages, i.e. simple black and white programs.  We make a real effort to make sure the fliers use a lot of white space; not many have dense edge to edge color. We may have printing more pages recently, but we've been going through black toner at easily twice the usual rate, and I don't think we've increased printing nearly enough to justify that.

Two questions -
On the page that that lists the number of impressions  - is that number of impressions over some period time, like maybe the last 12 months, or the number of impressions made by the drum, or what?
On the color usage page, jobs are listed for the past month - is it possible to set so I can look back at the last six months?

Thank you so much for your input!
Its deeply appreciated.