In papers by Castagnoli et al. and Van Lint, cyclic codes with repeated roots are analyzed. Both papers fail to acknowledge a previous work by Chen, dating back to 1969, which includes an analysis of even, length binary cyclic codes. Results from Chen’s study are presented.
Robert H. Morelos-Zaragoza. "A Note on Repeated-Root Cyclic Codes" Faculty Publications (1991): 1736-1737. doi:10.1109/18.104351