  Eruptive variables are young stars that show episodic variations of
brightness: EXors/FUors variations are commonly associated with enhanced
accretion outbursts occurring at intermittent cadence of months/years (EXors)
and decades/centuries (FUors). Variations that can be ascribed to a variable
extinction along their line of sight are instead classified as UXors. We aim at
investigating the long-term photometric behaviour of three sources classified
as eruptive variables. We present data from the archival plates of the Asiago
Observatory relative to the fields where the targets are located. For the sake
of completeness we have also analysed the Harvard plates of the same regions
that cover a much longer historical period, albeit at a lower sensitivity,
however we are only able to provide upper limits. A total of 273 Asiago plates
were investigated, providing a total of more than 200 magnitudes for the three
stars, which cover a period of about 34 yr between 1958 and 1991. We have
compared our data with more recently collected literature data. Our plates
analysis of V2492 Cyg provides historical upper limits that seem not to be
compatible with the level of the activity monitored during the last decade.
Therefore, recently observed accretion phenomena could be associated with the
outbursting episodes, more than repetitive obscuration. While a pure extinction
does not seem the only mechanism responsible for the ASASSN-15qi fluctuations,
it can account quite reasonably for the recent V350 Cep variations.
