Z-Cars further spin-off entitled "Second Verdict" in which Barlow and Watt looked into unsolved cases and unsafe convictions. Frank Windsor made a final appearance as Watt in the last episode of "Z-Cars", "Pressure", in September 1978, with Robins (John Phillips), the Detective Chief Superintendent from the original series who had risen to chief constable. Jeremy Kemp, Brian Blessed, Joseph Brady and Colin Welland also appeared, though not as their original characters. "Z-Cars" is incomplete in the archives. The period 1962–65 is reasonably well represented; though with big gaps. With the 1967–71 sixth series, when the programme was shown almost every week,
Z-Cars less likely to be recovered, as they were never telerecorded for a repeat or export.. When "Z-Cars" returned in 1967 in its 30-minute, twice-weekly format, it was on nearly every week of the year, which may account for its poor survival rate over this period. The 2 x 30-minute format gradually interchanged with the returning 50-minute format and when the 50-minute format fell into regular use by the series, this coincided with an increase in its survival rate. All episodes from the 1975–1978 period are preserved in the archives. BBC Archive Treasure Hunt was a drive to seek out missing