from 2000 ➡︎use 特開 before 2000 平 of 特開平 means 平成(昭 of 特開昭 means 昭和) https://rnavi.ndl.go.jp/research_guide/entry/1ipdl.php

I didn't know the words you questioned, so I looked them up on the internet. They are the words used in applying for the patents. According to the site, each application receives an individual number. Eg. 特開平１１－１２×××号/特開２０００－１２×××号 http://jp.aigipat.com/dict/t_74.html I am sorry I couldn't find out the difference between 特開 and 特開平