This morning another group published a historical analysis of light changes in "Tabby's Star", from archive photographic plates taken at the Sonneberg Observatory, Germany. (PDF here
; abstract here
In January this year (Schaefer), an analysis of archive plates from the Harvard Observatory suggested that "Tabby's Star" (formally, "Boyajian's Star") had faded rather consistently at 0.164+-0.013 magnitudes per century. However, this analysis was acknowledged to have problems, not least a period of reduced observation frequency in the 1960s, the so-called "Menzel gap", when organizational changes reduced the observatory activities. (With images taken over a century of development in both telescope technology and photographic emulsion technology, any long archive series is going to have problems. This is no criticism of the Harvard programme. However, it does show why the single-instrument approach of Kepler was taken and has been so productive.)
The obvious thing to do is to re-run the analysis using a different original dataset. This has been done using a library of 275000 plates taken at Sonneburg. After a processing pipeline described in detail (details matter in photometry!), two datasets were acquired, in "red" light ("pv" waveband) and "blue" light ("pg" waveband). Further analysis rejected correlations between brightness in different terrestrial seasons (does the observatory's atmosphere change between seasons, or temperature affect the emulsions? You don't know, so you do check.). Which camera (14 are part of the Sonneburg survey programme) was used for each plate also produced no correlation with the magnitude.
"This result is consistent with no dimming of the star between 1934 and 1995."
Which is in direct contradiction to the earlier results from the Harvard plates. However it does remove one aspect of the peculiarity of "Tabby's Star," replacing it with questions about one or other of the sets of archive plates. However, the uniformity of the data set from Kepler remains, leaving "Tabby's Star" as a very peculiar object.