In reference to the patent: USD779828
I would like to know how this patent differs from previous trolley bag patents. See below Patent dating back to 1996.
The most obvious difference between USD779828 and US5531366 is the first is a design patent and the other is a utility patent.
Design patents only cover the ornamental design of a functional object, not function. Thus most design patents consist mainly of drawings and very little text. The claims usually just refer to the drawing. Something like "1. The ornamental design for a container, as shown and described.". The original Coke bottle design patent D48,160 is a classic example. This Wikipedia article may be helpful.
Utility patents cover something inventive with utility. There is a need to be novel, useful and non-obvious. Utility patents are usually longer, have an abstract, a background section and detailed description about how to implement the invention. In particular the claims section of utility patents are usually quite detailed and specific in their description of what is patented.
The interesting part of this question is whether US5531366 should have been considered prior art for USD779828. According to Section 1504 of the Manual of Patent Examining Procedure, it sounds like it could have been considered as prior art.
Novelty and nonobviousness of a design claim must generally be determined by a search in the pertinent design classes. It is also mandatory that the search be extended to the mechanical classes encompassing inventions of the same general type. Catalogs and trade journals as well as available foreign patent databases are also to be consulted.
US5531366 is not cited in USD779828 so it is likely the examiner didn't consider it when granting the design patent. I agree with the questioner that the drawings in US5531366 are pretty similar to what is shown in USD779828 and probably should, at least, been considered by the examiner. I am not a lawyer so I cannot comment on whether or not USD779828 should have been allowed.