It's a load of PC Mumbo jumbo really.
The reg came into effect in Sept 99. How many kits have AP sold since then that came with DS2500 pads???
Also looking at the rules I think it only applies to cars still using OEM caliper set up - not if you have fitted an after market set up!
Kit I bought was supplied brand new to its buyer in 2010 with DS2500 pads. If they did this with reg90 being in place since 1999 then surely they are ok?? 
Or does that mean fitting AP kits are actually "illegal" On a road car??
Found this http://www.apracing.com/drawings/Individual%20Product%20Sections/2012_Brake%20Pads.pdf
Looks like AP say the DS2500 Is ok for road use like the APF404 pad they've released
....AP themselves supplied and fitted my BBK at Coventry in September 2006 and the kit was originally supplied with DS2500 pads and there was no mention of Reg90 to me. I continued to replace pads with DS2500's until AP advised I could use their own new pad which I am now running - In my use I have not been able to notice any difference other than a bit less brake dust.
AP tend to test their road brake kits for thousands of miles on their staff cars. They have a very long and well established reputation for excellence and do all they can to uphold it.
When I became aware of the Reg90 'illegality' I was of course very concerned and spoke to Pete Cullen (AP's Senior Engineer and who had fitted my BBK) specifically about it. He assured me that as the DS2500's were supplied with my AP kit and the whole kit was designed to work together as a whole, I would not have any problems.
So, I'm adding further confirmation to what you are saying, Lee
