Virtually all patents cite "prior art," or previous patents that are relevant to the new invention.

In 1836, The Patent Office also went back and renumbered all previous patents with a suffix "X".

The patent office normally looks at previous patents for prior art and doesn't have the means or time to conduct a complete search.

Several previous patents have been issued to inventors who described different approaches to the mystery.

This patent incorporated the developer's previous German patent.

Another patent was filed posthumously in 1877 by his wife as No.194,278 on improvements of Werner's previous patent.

Judson made a "C-curity" clasp-locker fastener in 1905 which was an improved version of his previous patents.

During this period they also confirmed previous patents and deeds.

The patent examiner takes a look at the specifications of your product to guarantee they don't overlap with previous patents or inventions.

Novelty means it's different from the prior art (previous patents or something known to the public).