Every so often it happens, you can always "challenge" the lack of fill, but most of the time, the response will be "there were orders ahead of you". Few months back, I suggested an OB on SKX at $5.35 and at least three "threadsters" used the same level, I did not put my own order in for a day or two, the stock got beaten and these three guys had their orders ahead of me and got the LOD at $5.16 because they were "ahead" of me. I had no reason to complain, since I got $5.35, but in PM's some of those mentioned they got a better price than their own GTC, so these things, sometimes, cancel out.
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