From the diary of Dr. Bard:
(original timeline September, 1923)
"...however there are singular voids springing up in time; lone characters missing in a world oblivious to their absence.
"Where is da Vinci, for example? No one from his own point in history seems to have the slightest knowledge of his existence. His works, the records of his life, spring into being later in time. The first literary mention I can find of him is in 1863. A travel to one year later, June 1864, finds him once again a pivotal point in the (First) Italian Renaissance; his name altering preexisting scientific and secular writings.
"Conversely, where is the work and records of Jonas Peerman? The man who alleviated many of the woes of cancer - stumbling by chance upon the medicinal shrub, 'Calapus arboreus'. After a brief period in the late 2200s, he and the plant disappear from history. I have checked in twenty year intervals from 2220 - 2380.
"Has someone else used the door?
Will I, at some later date, create these holes in time?"