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Hi Chris.. If I understand what your asking correctly you have nothing to worry about. Marks on the back of the mirror are normal. Often marks are made a registration points or other info when the mirror went through it's grinding.
If you have a black dot in the center of your mirror when looking inside of your DOB from the top, this is also normal. Some have a dot and others a small circle. This is used to collimate your scope. The very center of the mirror tends not to reflect light into your secondary mirror and is not seen when viewing objects.
Hope this helps with your questions
Mardy
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