Are the plugins/Project64 forwards/backwards compatible?
This is fairly confusing to explain but here goes: the 1.4(&1.5) application is backwards compatible with all public versions of the plugin specifications, so you can use for example the v1.0 video plugin in 1.4 .exe if you wish. The plugins however are not backwards compatible, so for example you cannot use the 1.0, 1.1 or 1.2 application with the 1.4 plugin (but you could use a 1.3 plugin with 1.4 app, because both 1.3 and 1.4 share the newer 1.3 specification, all previous versions were to the 1.2 spec.). The other types of plugin should be compatible across all versions.