When I used to have new tyres fitted years ago, I remember pieces of lead crimped on to the rims for balance. With the alloy wheels I have these days I'll have to have a look see if anything is there.
wheels balanced "on" the car required a sit on machine scooted up to the wheel (vehicle jacked up) spun up the wheel and balanced the wheel brakes & hub, vary rare.
steel wheels balnced off the car with crimp on wieghts inner & outer rim
alloy use stick on weights & a good fitter can place them inboard of the external spoke face.
Loving the site.