The progress bar is correct until 10000 steps, yes. And up until 10000 steps, the step count is shown using the full number.
When the watch was first released, I used to see “K” for thousands under 10000, but that stopped at some point. Maybe they changed that in the November update?
What happens now is that you don’t see “K” until you reach 10000. Once you reach 10000, you see “10K”, “11K”, etc. So, it looks like this:
6492 steps: 6492
8531 steps: 8531
9999 steps: 9999
10000 steps: 10K
10099 steps: 10K
10100 steps: 10.1K
10615 steps: 10.6K
13824 steps: 13.8K
It shows the K only after 10000 steps, and it shows a decimal (for example, 10.1K) when the hundreds place is >= 1. So, 10K for 10000 - 10099, 10.1 K for 10100 - 10199, etc.). You can still see the total step count if you launch the “Fitbit Today” app, so the total step count is still kept somewhere, it just doesn’t show on the watch face. I don’t know if Watch Face Studio has access to the real step count or not.