During earlier years, all the objects under the "Cisco MIB" branch were documented in one monolithic document. This document was updated with each new version of IOS. Therefore, there was a 9.0 "Cisco MIB" and a 10.0 "Cisco MIB." In those days, the product line was exclusively routers.
However, as IOS matured and the product line, grew this monolithic MIB model quickly broke down. Within one revision level of IOS, there were different versions, such as the IP only image and the IBM feature set version. The product line also included other devices such as LAN switches running completely different IOS.
Starting with IOS 10.2, the monolithic "Cisco MIB" was broken into component MIB documents, each focusing on a specific feature, technology, or device type. This structure allows quicker implementation of new features. It also allows users to compile only the parts they need into their NMS.