While nobody knows let's look at this with a sense of non-political common sense. At 1st fearmongers touted that all flights into and out of the UK would cease totally on the 29th. When this was both laughed at and ridiculed ( by those on all sides) it was replaced with 'only flights by airlines with an EU presence will be allowed to operate' this also didn't stand up( although worth noting that most airlines created some new holding companies to assign certain stock/ assets too just to be safe). Then there was a variation regarding companies % of stock being in X or Y location ( UK or EU). Now we are where the @
the810 mentioned above where a fallback position is being publicly touted that things will carry on 'as is' for 9 months ( although that period is being mentioned as being extended already) where nothing will change but UK carriers can't increase on what they currently have.
Now lets be, no matter which side of the fence we individually sit on, be realistic for just a moment. The chances of the EU saying no UK carrier can land in any of the then remaining 27 member states & that they will prohibit EU carriers to land in the UK( obviously it's a two way thing, right
) until new legislation, standards and agreements can be sorted out ( I believe the current period being mentioned is 3-5 years) is imho beyond laughable and below a 1 point %. The impact on business both UK & EU will be far too high for anyone to stomach ( us Brits / UK immigrants are pretty big travellers on the whole) & a solution whilst apparently not known at this point will be found as miraculous as that blatantly obvious suggestion is to some. Whilst again trying to avoid a political discussion I am reasonably confident that once the day has come and it's realised, if not willingly accepted, by all then those obstacles which have been thrown around since the day after the result will find a way to either disappear or be overcome one way or another. Something of important note here is that BA, along with several UK carriers have increased not only regularity but also added new EU destination routes to 2019 schedules. Would they really be doing this if they themselves thought X destination was going to become outlawed mere months after implementation. The costs in assessing a new route, the contracts, legal implications & obligations and last but not least the costs involved would suggest that such moves were made with reasoned confidence of a resolution or maybe the heads of all those airlines have collectively totally lost the plot & placed their airlines at risk just for fun all at the same time?!
When it comes to the, notable, issue of X flight being an addition on previous quotas I imagine there are sites which detail historic flight numbers/ details for at least the last few years somewhere where you could cross ref' your bookings flight numbers/ times etc to establish if it's established or new and look at adjusting your travel pans if need be( we'd be talking a matter of hours here in the vast majority of cases) I've never paid that much attention to such things but if they do exist then FT is gonna be the place where someone knows about them.