Angelo regenerating at the beginning of Series 3 was borrowed from Doctor Who (1963). Tyler Butterworth was replaced in the role by Tim Whitnall who played Angelo up until the finale.
Shelley Thompson (Rita King) remained in the series until Series 6 and was replaced by Katy Murphy as Katy Andrews who remained until the finale.
Michael Benz replaced Matthew Wright.
The 1999 series explained what happened to Mike Mason and that Mike Mason went off to America and Angelo and Katy reading a postcard he sent them.
Steven Geller died in 2015.