I think you are right. The first rear-locking 60* bolt rifles had metal trigger guards and magazines and wood stocks. There were luxus and standard models (was it SL, M and S action lengths or something?). My 'professional' was a synthetic stock and trigger guard version of this.
Now I believe all the current generation with SBS bolts (3 position bolt) are all plastic or makrolon trigger guards as you said, whether wood or synthetic stocked