These episodes are from season one, which are the five black and white episodes that were originally 'interspersed' with the colour ones. This was because filming had been interrupted by the infamous Strike which had resulted in the said episodes not being done in colour. As a consequence, they have become much sought after and rarely seen. They were only ever aired the once by ITV - their original showing, despite any subsequent re-runs of the series there may have been. As Jean Marsh (Rose) once told me; these black and white episodes were among some of the best that were ever done! They will also help to fill in gaps for those who never saw them, and as to what happened during those missing years: 1903 - 1907, and also will reveal the destiny of some of the characters that appeared to 'vanish' for no apparent reason; some of whom later returned, and others who were never seen again...
This first season is what certainly resulted in 'Upstairs, Downstairs' taking off in the way that it did, and becoming such a massive success. It was an immediate 'hit' with the viewers, and the closing episode which left the son of the household involved in a scandalous affair with one of the housemaids, and the daughter, his sister, marrying a homosexual poet, was certainly guaranteed to bring viewers back for the second season!