As they say... "the devil is in the detail". For what it's worth, this is my humble opinion.
In answer to "Andy R" and "What's a Girdler" - I wouldn't worry about exceeding the requirements. So long as the requirement of at least 300nm is satisfied, and the trip includes two full stop landings at aerodromes different from the aerodromes of departure, then the requirements are satisfied - wherever those aerodromes may be, and whether or not you eventually return to the point of origin.
I think the way to interpret this is to look at the phraseology.
Define "the aerodromes of departure".
Note the use of a plural, "aerodromes". This means that each take-off, (a: Point of Origin, b: Aerodrome 1, c: Aerodrome 2 etc), is, (or becomes), an "aerodrome of departure". So all your subsequent landings, (on this cross-country flight (singular) of at least 300nm), must be at a different aerodrome to any of the ones (plural) you have previously departed from.
This rules out Scenario 1 from KeyGrip's Question, since the cross country included a landing at the point of origin, which was a previous point of departure for the sortie. So I would support "PowderMonkey's" view that this in practice means a "round trip", although I would say it is optional whether the airborne section of the return to base leg is included in the 300nm total or not.
I would have thought Scenario 2 (with the overnight stop) would be ruled out mainly for one and potentially two reasons...
a) There is no such thing as Night Time VFR in JAA world, (albeit there is in FAA land), so for qualifying as "a VFR cross-country flight" (singluar - meaning a single sortie), they could eliminate any time logged as "Night" as not satisfying the "VFR" requirement for JAA purposes. Now the times KeyGrip gave, would not in themselves imply any night flight, but then how can a single VFR cross-country sortie be said to continuous throughout the hours of darkness, with the plane sat on the ground?
This is not to say, however, that a Sortie from A-B-C which satisfies the requirments in total, could not include a night stop at C before returning to A in the morning. That should be valid.
b) Even if the whole trip was conducted in a single day under VFR, having flown 276nm from A-C-D does not (obviously) satisfy the 300nm requirement. The trip then continues back to A via C. If, as KeyGrip says, C was 145 miles from D, and a landing were made there on the way back, then I would say the requirements would be fulfilled.
But if we change the scenario slightly, and move C to less than 24 miles from D (say A-C = 256 and C-D = 20, total still = 276), then Landing again at C on the way back would invalidate the requirement: "...300nm in the course of which... (land) ...at an aerodrome different to any of the aerodromes of departure".