All righty then, I've had a bit of time to address this.
So, AP is not the same as diacetyl, obviously. Most vapers treat the two the same but they are not. 2500ppm is more than trace amounts. Is it significant? Yes and no. It's definately enough to say AP has been added. It's not enough to deem it as a definate health concern for me.
I cannot find a OSHA PEL for recommended workplace limits for AP in the US. There is none for diacetyl and acetoin. I don't think there is one for AP. I think they are still working on one. My google fu gave the source for your numbers, I think. I found them on the Cloud Nine page. They do say "The published occupational safety limit of AP is 135µg (135 parts per million)". They also give one for diacetyl, "there is a published occupational safety limit of 66µg (66 parts per million)". I believe these are EU or UK numbers. Not US numbers. That's why I needed time to respond. My prior reading on the subject lead me to believe there were no safety standards for diketone inhalation in the US. I needed to verify.
https://www.osha.gov/dts/shib/shib10142010.html
You'll want to know why I don't see it as a definate health concern. While, as you point out in the manner that Cloud Nine did, there is 2500 micrograms in a ml of juice and the EU or UK recommends inhaling less than 136 micrograms in a day. Having 2500ppm(I don't want to type micro grams every time) in a ml does not necessarily mean we are inhaling 2500ppm for every ml of juice we vape. I don't know how much of that survives being turned to a vapor. It has not been studied. I'm not saying it is not a health concern. I'm saying I don't know if it is a health concern. The UK or EU, who ever's numbers those are, see AP at roughly half the risk as diacetyl as far as volume. The inhalation recommendation for AP is double that of diacetyl. What we need, if the goal is to stay somewhat in the limits of a recommendation on amounts, is to know the AP ppm of the vapor, not the juice. It's my guess that it's no where near 2500.
I hope that helps.