Indeed overspeeding is not there... Or technically is very momentarily... The issue is we compare in built loco Speedo with GPS Speedo
N both have shortcomings...the loco Speedo has some limitations and is affected by various factors... But at the end that is the reference point for LP and IR... So even is actual true speed is say 132 but loco Speedo says 130... It's officially not overspeeding as reference is loco Speedo..
At times it might shoot up for few secs but is actively controlled back by LPs
N...
more...

coming to GPS Speedo... While I have myself tracked n reported screenshots from my SK trips where it shows 130+ and for extended time over larger distances... There is a catch.. GPS Speedo is only as accurate as the GPS devices.. Most high end smartphones today deploy multiple methods for GPS (AGPS, cell assisted, Glonass, Beidou etc).. And the accuracy also depends upon GPS signal quality... Mostly such phones have accuracy of 1~2 Meters.... Some other phones ESP low end could have accuracy of 7~10 Meters
So that means even with say 1 m/sec diff you could have a deviation of 4-5kmph (so when GPS says 134, true could actually be 130 or even 129)..
Using moving average as reference rather than just the max over short distance gives more accuracy...but again if GPS signal is lost momentarily (even 1~2 secs) data accuracy reduces... Still moving averages are fairly accurate n I have checked that on my trips as well...
As a Traveller though we have only GPS Speedo as our ref and get excited to see overspeeding on it (including myself 😀😀)