@idrougge
Depends on your interpretation, I guess (i.e. the info. available about WB development, whether AmigaDOS should be demarcated from Workbench or not etc. ; cf.
this AmigaOS article). You might have to ask Tim King about the extent of direct contributions (if any or even if minor) to WB itself. He strikes me as the kind of guy, though, who wouldn't have been too bothered if he directly contributed and didn't figure in the hidden credits.