A poly(dimethylsiloxane)-co-poly(hydromethysiloxane) (PDMS-co-PHMS) polymer has been characterized with respect to chain length distribution, heterogeneity of chemical composition, and sequence distribution using SEC, H-1- and Si-29 NMR, and MALDI-TOF-MS. Due to ambiguities in the peak assignment the deconvolution of the mass spectrum into the bivariate copolymer distribution is not possible. Alternatively, the expected mass spectrum is computed from the SEC and NMR data. It is then mapped onto the measured one, and an almost perfect agreement is found within the peak resolved low molar mass range, leaving only a small number of adjustable parameters. As a result it could be shown that a large number of chains contain no functionalizable units at all.