Accidental inventions aren't entirely accidental. The circumstances leading to their inspiration may be accidental, but the actual invention is not.
Take penicillin for example, while the discovery of the mold growing inside a Petri dish is accidental, the recognition that the mold was secreting a substance that kills bacteria and the idea to mass produce this substance in order to treat human beings is not.
With X-rays, even after the discovery of X-rays, work still had to be done in order to figure out that x-rays can be used to medical examination and work had to be done to build an x-ray machine that can take x-ray photos of people.
For Silly Putty, the invention of Silly Putty was accidental, but the idea to put it into plastic eggs and sell it as a toy to children is not.
A lot of work goes into an invention even after it's accidental discovery. The discovery has to be recognized, it has to be applied for some use, and it has to be mass produced for the public. The accident is only part of the process that goes into an invention.