the "hot" teapot remained in use at the hotel for several weeks .....
How many others got ill or died?
The radiation from the polonium warmed the tea it was reported. Wouldn't the fellow who put the stuff in the tea be almost as bad off as the victim?
I wonder how much danger the pot held after it was emptied and washed.
Anyone else served from the same teapot till it was emptied and rinsed. Those served after that would get progressively smaller doses. A smart assassin would not have much tea prepared in it [to minimize the traceabilty], so it is likely that the amount was small and the teapot was rinsed pretty soon after the intended use.