3 Point,
You seem to forget that flying solo can be done in two ways;
1. As a student authorised by and under the supervision of a Flight instructor and meeting all the requirements such as licensed aerodrome etc; or
2. As a qualified pilot exercising the privileges of their licence, medical and ratings they hold
All the examples you give require dual training only. There is no solo training required as part of any differences training or for renewal.
With the differences training, the pilot can not fly as P1 even solo until you sign off the differences training as being fully completed to the required standard. To do otherwise would remove the requiement for differences training before flying a single pilot tailwheel type to be certified would it not?
However, if you are an FI then you could effectively send them solo under the same conditions as a student and one of those conditions are that it is a licensed airfield.
Remeber also that all JAR training must come under an RTF/FTO and they should have clear requirements for the authorisation and supervision of solo flights.
Regards,
DFC