Multiple Timelines?

SM Stirling's The Peshawar Lancers and The Sky People are set in different alternative histories but this could nevertheless make them installments of a single series since The Peshawar Lancers, like many other works of sf, assumes the coexistence of divergent timelines. For example, Poul Anderson's many series include not only future histories and historical fictions but also several interconnected alternative history novels.

In both The Peshawar Lancers and The Sky People, Terrestrial history diverges from the course of events known to us because of celestial events: 

comets strike Earth;
life has evolved on Venus.

I thought that history in The Sky People had diverged from ours in 1962 when a Russian Venus lander transmitted an image of a Neanderthal. However, before that:

in the late1940's, microwave observations had provided evidence of Earth-like surface temperatures;
in 1932, infrared studies had shown that the atmosphere was possibly oxygen-nitrogen;
in 1927 and 1928, ultraviolet photographs were taken although we are not told the results.

Googling discloses an article by Ross (named in the novel) on the 1927 ultraviolet photographs so it seems that, from the point of view of Terrestrial history, this timeline diverged from ours after 1927, possibly in 1932, whereas, from the point of view of Venerian evolution, it diverged billions of years ago. Similarly, in The Peshawar Lancers, that timeline diverged not when the comet or comets struck the Earth but when cometary orbits had taken a different course at a much earlier date.