Using molecular dynamics simulations we show that a given monomer in a miscible polymer blend experiences broad distributions of both connectivity driven self-concentrations and thermodynamically controlled intermolecular concentration fluctuations. While these distributions should play a significant role in determining the constituent's dynamics across the whole concentration range, the distribution of self-concentrations is particularly important in the dilute limit, where intermolecular concentration fluctuations should be absent. These conclusions allow us to rationalize the recent literature results that report the apparent self-concentration determined in the dilute limit surprisingly depended on the blend partner.