Antiques: Painting's auction value sails in uncharted waters

Q. This beautiful oil on canvas is part of our Mom’s estate. She bought it in the 1980s. The artist is Ivan Aivazovsky, 1817-1900, titled “The Sea”, and was apparently painted around 1860. 
It has some documentation including a certificate of authenticity – part of which was done by the Artistic Commission of Tretjakov Gallery in Moscow, 1971. It was initially bought directly from the artist and was in one family’s hands for 70 yea