Firstly Group A ceased to exist over 10 years ago. You are quite right there is a confusing plethora of information floating about, some caused by the CAA who couldn't grasp that most Microlights are actually Single Engine aeroplanes driven by a Piston engine. You can fly them quite legally under the UK ANO on a SEP class rating on either a UK or UK issued JAA licence. Differences, or familiarisation training is advisable, but not mandatory.
The rules do differ from country to country as a result of different definitions and licensing requirements. JAR-FCL 1.005 contains a statement that has attracted a number of different interpretations
(5) Whenever a reference is made to
aeroplanes this does not include microlights
as defined nationally, unless otherwise
specified.
This does not have any legal status in the UK, and was primarily to prevent hour builders logging time on aircraft that might not even need a licence to fly.