Hi Alex,
I think you would find Skymap very useful:
http://www.sky-map.org/
At the positions you have drawn (or within 8 arc-minutes) there are no apparent galaxies or other nebulous objects (down to about 18th magnitude at least), so this would seem to be, as you have noted a spurious observation. That's not a criticism, in any way, our eyes and imaginations sometimes do play tricks on us at the edge of the envelope -- even for experienced telescope users. We all sometimes make mistakes or incorrect assumptions -- that's human nature.
There's no better (or more curious) case of this than Baxendell's "unphotographable" nebula -- NGC 7088. A non-existent "nebula" near M2 in Aquarius that was originally reported by Baxendell in 1880 and "observed"
by Dreyer (1885, 10-inch refractor)(Included in the NGC as NGC 7088), Bigourdan (1897, 12-inch refractor), Hagen (1915 and 1917, 16-inch refractor), Wolf (1927, 6-inch refractor), O'Connor (1929, 15-inch refractor), Becker (1930, 12-inch refractor) and Lehner (1930, 4-inch refractor). But never showed up on any photographs of the area -- no matter how deep the image.
It was later concluded that it must have been some sort of strange internal reflection caused by nearby M2.
Curiouser and curiouser, in the 1980s it was reported again by a few prominent U.S based Deep Sky Observers (it was still being marked on maps even in the 80s and 90s) and described in near identical terms to Baxendell's initial observations. I remember well the ferocious storm that erupted over claim and counter claim that is was or wasn't real (and who was lying and who wasn't) -- unedifying.
Some claim it might be a bit of IFN (integrated flux nebulosity) at high galactic latitude but even so I does not **ever** show up on photos no matter how deep. It must be spurious -- there is no other explanation.
I have spent a total of about 30 minutes using both 10 and 18" 'scopes checking the alleged location and for me there was nothing at all that could be described in any way as "nebulous" in the area. There isn't even any field irregularities (a clump of faint stars or an area where there is an over-abundance) nil, zip, nada. Deep images show the same.
That's a quite of list of famous and otherwise credible, capable but clearly mistaken visual observers who said they saw it --Dreyer, Bigourdan Hagen, Wolf, O'Connor, Becker & Lehner!
As for the U.S observers in the 1980s, I won't name names (until they're all dead!)
Best,
L.