Information on decoding the 1 to 6 digit code has been published in: K. Shirriff, C. Welch, A. Kinsman, "Decoding a VCR Controller Code," Cryptologia, 16(3), July 1992, pp 227-234.
A program to do the decoding (not written by the above authors) is available by anonymous ftp to wuarchive.wustl.edu in /usenet/alt.sources/articles/7000-7999/7020.Z