1918 was a terrible year. I don't think that at the time there were any files to be discovered, everything must have been in terrible disarray.
Letting my imagination run, I think that the abdication paper in question might have been a rough draft of the final abdication document.
In any case, at the time the information might have come from Soviet sources and I don't think they can be fully trusted.
On the other hand, the riots and the defeat in the war against Japan might have been too hard to swallow at the same, time and perhaps the thought of abdication might have crossed the Emperor's mind, which is doubtful. He was raised to be an autocrat.