That's normal. It's also technically not the real speed, as if you would measure it with GPS. there are so many influencing factors in the game, that there is a variation.
has to do with the resistors, transistors, microchip, wire resistance from speed sensor to computer, speed sensor, even temperature or wheel diameter- yes- even profile is a factor.
I see this in mine too, where - for my eyes- it seems like the analog instrument shows 1mph higher than the digital gauge. now- I can't say that the digital reads for example 70,95 mph - it just shows 70.
I would not see it as an issue. Also- the difference if you have km/h is lot higher than in mph. There is also the tolerance which says on full scale the speed can have a variation of 10%. this means up to 7km/h / 3mph difference is very good. Would be too much to go into detail. I hope that's ok.
I don't look that specific to the instrument. and since I love the center display, I rarely look at the analog instrument- only when the display shows me for my feelings 10 minutes, that I turned off my cruise control.
I would not worry.