How did you count the IDs - by callsign? There is no way to prove completeness and correctness in general for an airline, you'd need access to their records probably. Most public databases are always lagging or incomplete, although with manual work you can normally get a very good picture. Since both the UK and Ireland however publish their registers, you're in luck for those two airlines, e.g. this should be fairly good for Ryanair: www.iaa.ie/commercial-aviation/aircraft-...nd-monthly-changes-1
That said, as far as truly invalid IDs go, where did you get them? If they are seen sufficiently often and over longer time periods, then they are at least real.