According to GOL, Laser Atlanta is 238 pps. Stealth mode sends 2 out of 7 pulses (=68 pps). I tested at 256 pps, same 2 out of 7 pulses (=73 pps), so it's pretty close in terms of frequency. I would assume that not detecting stealth mode is not a matter of frequency, but filtering.
I tested my 8500 X50 v6.1 with a microcontroller connected to a GaAs (940nm) IR LED. Duty cycle was 25%. The frequency was obtained by dividing a 32'768 Hz crystal.
This was unexpected, as the veilguy tests showed the X50 (unknown version) didn't detect stealth mode. I have also seen a video of yet another X50 not alerting to stealth mode - while the V1 beside it did.
BTW, I just wanted to test my detector, as I hadn't had a laser hit on it. I programmed 128 pps, then 256 pps, and then thought why not - stealth mode!