Partime, Could be a common 210 not sure how to distinguish between the two. Also, not sure if it's a plate drip due to crisp edges without ink stain inside error. Thinking it could be a foreign object between plate and stamp. There were over 600 stamps and this was the only one that had this mishap.
A plate drip is pretty interesting, and if the cost isn't too much, I would collect them just for fun. However, you could probably make your own without much effort.
As far as evaluating your stamp, the common advise is to always assume you have the least valuable version, then work from there. Doing it this way tends to ground newcomers in reality quicker than assuming the highest value, and then be told (by many) that you are wrong. Best is to say, "This looks like a 210 (the common version) but I think it may be a 211B because ..."