A few years back when I normally visited the H&K forum, there were multiple horror stories about botched trigger work on H&K pistols from Bill Springfield. To the point where multiple members reported having to send the pistols back to H&K to have the factory parts installed back into the pistols in order for them to be safe and function correctly.
I'd suggest you open that pistol up and find out what exactly he did to it. I'm curious how you make a trigger pull "shorter" on a DA/SA pistol. Are you talking about reset, overtravel, pretravel, or overall trigger pull length? Find out what weight spring he used on the striker. Find out if he messed with the firing pin block spring. Find out if he messed with any other springs. Find out what parts were polished or stoned.
The P99 has been on the market for around 22 years now. In those 22 years, Bill Springfield is the only known gunsmith I've seen advertise trigger work on these pistols, and in those 22 years, I believe this is the first time I've heard of someone actually using him on a 99-series pistol. These pistols generally have excellent triggers, that get much better after some use.
I really would suggest you find out what type of work was done on that pistol.