I have had the inspiration to connect my two eras of which I have already written with the next book. those familiar with my writing know that I now have a Western trilogy which is set between 1863 and 1878, with all of the major action and events between 1866 and 1871; and I have a speculative romantic adventure set around 2020. The time period of the latter was chosen so that the artifacts and cultural elements would be essentially the same as now. No specific year is given so as to make the book more timeless. There are many reasons to link the two, including a natural similarity between some of the characters even though they are distinctly different people with different personalities. A strong, logical rational for the modern characters to be curious about the historical ones exists.
So the question is: Does it in anyway negatively effect the 'brand' (for want of a better term) of the Western stories to link them to a future that may never happen? The major historical events really happened in the background of my fictional historical characters. The 'historical' events in the modern, speculative novel may never happen. Of course it is fiction, but does a link between them reduce the legitimacy of the historical series?