Resizing and headspace


So, I have a question about resizing and headspace that I haven't come across before. I bought a new 30-06 and loaded some new Hornady and Starline brass for it, took it out and fired it all and now am in the process of reloading. What is confusing me is that using the Hornady comparator I measured both the unfired new brass, and the now once fired brass and they are measuring the same with very little variance. I would have expected at least a few thousandths growth at the datum line. All the fired brass chambers fine into the rifle before any sizing. I am unsure what this indicates or how I should proceed. I ran the fired brass through the sizer die to make sure of neck tension but I was needing a bit of advice before I loaded them back up. Is this unusual or normal?
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