It's common for blems, ,just about every tube has something, depends on where it is in your sight picture and if you can live with it although after a while my experience is that you don't notice it.
Generally speaking, depending what size and which "zone" the blem is in, most people generally stop noticing them once they stop being fixated on the blem, and look "through" the NVD at the target, a lot of guys will get their new NVD and power it up and aim it at a white wall and notice a spot or two and their OCD will kick in, especially if they feel they've made a significant investment in the device. Most end up getting over it pretty easily once they actually start using the device for scanning, observation, and target engagement, but some find it more difficult than others to "look past" blems once they get it stuck in their minds that their new toy is "imperfect."
The reality is that you will rarely find a 100% perfect tube with no imperfections anywhere in the image. That being said, there can be a big difference in between the same size blem in the middle of Zone 1, versus the edge of Zone 2, moving into 3.