There is always a whole lot of chopping and changing of the coming year’s flying plan at this time of year. They tend to need to have a clear idea of the plan for internal movements before they can finalise plans for new recruits, and as a result there is always a lack of information and then a sudden mad rush to train up new recruits. I am sure the Brexit shenanigans, constantly changing ongoing 787 engine issues, pilot strikes, general global economic outlook, and plenty of other variables are causing real headaches for the planners just at the moment.
With regards to who is spending ages in the hold pool and who is not, and what those reasons are, if indeed it is even happening; there really is no point in even asking the question, never mind worrying about it. BA will do as they please and you would have a job on your hands changing the process from within, never mind as an aspiring employee. For what it is worth, the latest figure I have heard is 300 new recruits for next year, so you will all be in soon enough.