We use a 3D SCF model of polymer adsorption to investigate the adsorption of A-B copolymers from A-B/homopolymer A mixtures onto planar substrates composed of two chemically distinct randomly distributed sites, one of which has a preferential affinity for the B segments of the copolymer. Our results show that when the chemically heterogeneous substrate motifs are recognized by the copolymer, the copolymers can transcript them with a relatively high fidelity into three dimensions. The way the surface motif is transferred is strongly dictated by the copolymer sequence. We show that block copolymers are capable of detecting small clusters of the substrate adsorption sites. The fidelity of the pattern shape and the distance from the substrate to which the pattern gets transferred increases with decreasing the length of the adsorbing block of the copolymer. Our results also indicate that increasing (i) the interactions between the copolymer adsorbing segments and the "sticky" points at the substrate, and/or (ii) the repulsion between the copolymer segments increases the total adsorbed amount of the copolymer at the mixture/substrate interface but it decreases the fidelity of the substrate chemical pattern transfer into the mixture. We show that, in contrast to the block copolymers, macromolecules with alternating sequence distributions adopt different conformations on random substrates in that they tend to localize at the boundaries between the C/D surface sites, where the substrate chemical pattern more closely matches the sequence distribution of the B stickers along the copolymer. We claim that this feature allows us to use alternating copolymers in situations where one needs to suppress the chemical pattern transfer on such random substrates.