Described herein are compositions and methods for the production and quantification of barcoded or unique molecular identifier (UMI)-labeled substrates. In one aspect, the substrate is a bead comprising a template oligonucleotide that is elongated by successive extension reactions to provide a bead with an oligonucleotide comprising a plurality of barcodes and conserved anchor regions. Methods are also described for quantifying the amount of template oligonucleotide loaded onto the substrate and the products of the extension reaction after each round and after the final extension.