As to the X boat routes being constructed in 624 and not before - I think this falls into the trap of thinking that the Imperium is a static pre-planned entity. 'Historically' speaking this is clearly not the case. There is nothing to say that x boat routes were not re-drawn as time and technology went on.
An example is the English road system (I say that because its where i come from). For centuries people going from London to the north travelled on the old Roman road that goes east to Peterborough and then up north - the road deliniated the Roman territory.
In the 1950s the state built the Motorway system that was more logical. The new road north was the M1.
This didn't mean, however, that the great north road came to an end - it became the A1 and is as busy today as it always was.
I think the Imperium must be similar - it has existed for about the same time as England so as new technology progresses (i.e. in J space) new communications routes get 'cut'. However, this does not mean the old routes stop, just that quicker routes exist.
An example is the English road system (I say that because its where i come from). For centuries people going from London to the north travelled on the old Roman road that goes east to Peterborough and then up north - the road deliniated the Roman territory.
In the 1950s the state built the Motorway system that was more logical. The new road north was the M1.
This didn't mean, however, that the great north road came to an end - it became the A1 and is as busy today as it always was.
I think the Imperium must be similar - it has existed for about the same time as England so as new technology progresses (i.e. in J space) new communications routes get 'cut'. However, this does not mean the old routes stop, just that quicker routes exist.