I suggest naming the category of non-investigated or uninvestigated sightings "NFO's" or Non-investigated Flying Objects (NFO's). This is an indeterminate catchall category for initial incoming sighting reports prior to any Hynek screening or investigation. Most cases will fall into this category and never get reclassified as either IFO's or UFO's. The "NFO" term falls nicely in between IFO and UFO alphabetically which is conceptually where it belongs.
For simplicity I include all conventional explanations within the scope of the term "IFO" including cases where there is no object at all, such as some hallucinations and hoaxes. I don't quibble over hypertechnicalities of the "flying" term, where purists complain that we usually don't know if the object is flying using aerodynamic principles, and celestial bodies are not "flying" at all, etc. The traditional "UFO" term uses the word "flying" and everyone has a rough idea what "UFO" and "IFO" mean and they don't take it so literally. "NFO" nicely and logically alliterates with IFO and UFO so it will suggest the others.
Trying to replace the term "UFO" because of quibbles over the word "flying" will simply lose 99% of the people who have an interest in the UFO subject.
The Hynek screening process is explained in his basic textbook of UFO science, The UFO Experience, published in 1972 and endlessly reprinted in numerous editions ever since. You can buy paperback copies on Amazon.com for less than the cost of shipping so there is no excuse for serious UFO researchers not have it and read it.
No sighting report according to Hynek should get the "UFO" label until after a scientifically competent investigation has eliminated IFO's and other conventional explanations.
Whenever it is unclear what we mean by "UFO" or if there is a possibility of some confusion then simply say UFO Unknowns or "real UFO" or Unexplained UFO's or the like, just as we now do anyway.
With this new terminology the AF Project Blue Book statistics would transform to something like this (these are extremely rough approximations subject to refinement and more thorough statistics after Will Wise's BlueBookArchives can get all the BB files online so a more thorough analysis can finally be done):
NFO's - 10,500 (approx.)
IFO's - 1,500 (approx.)
UFO's - 3,000 (approx.)
Total - 15,000 (approx.)
I am being very conservative on the number of UFO Unknowns, as 20% of the total, whereas it is more likely as McDonald estimated, about 30% to 40% or about 4,500 to 6,000 Unknowns.
UFO's thus outnumber IFO's by at least 2 to 1 when we stop bastardizing the statistics by including non-investigated NFO's. Using Hynek's definition an investigation must be scientifically competent, hence very few BB investigations would qualify in his opinion and in the estimation of McDonald and others who have reviewed BB's work.