You need to distinguish the original Dutch type with physical separation between lanes (so they are often drawn as separate lines), and eg German ones with road markings only. I have seen a few of the former.
I believe this is only a matter of effort in micro-mapping. If someone has the time, they are welcomed to increase their level of detail in the spirit of iterative refinement.
UK has spirally marked roundabouts only. Circle physical center islands, not angled as in turbo-roundabouts.