[Sidebar]
The '6.2' client was before my time..but, it was still supported up until the last couple of years - and yes, it post-dates the '6.1' client
I think they were live updated clients, opposed to the disc or ddl (steam) clients we support now.
The reason it is still 'locked' in the code is that it's a placeholder.
Perl scripts are hard-coded with that value and removing that entry would throw off every script that makes use of that enumeration.