Hi Mark,
In terms of Slovenia, as this is new to the programme it is really early days to see whether or not we would be able to add additional dates to the calendar. But you could always ask again in a few months when we've had a chance to review the early numbers.
For Croatia's Makarska Riviera there is quite a range of dates as it is and it is highly unlikely that we would offer any additional dates. There is a gap in July and August as the prices are so high and the general demand to travel at this time of year drops (although we are aware that this is the only time that some of our customers are able to travel).
We try to keep an eye on all of our tours and dates each season to make sure that we can match demand and there have been occasions when additional dates have been added (for example a couple of the one-off tours ended up having extra dates added this year).
So I'm not really sure if I have answered your question or not but hopefully it's shed a little light on things.
Kindest regards,
Julia