I would expect most accountants are pretty reasonable in this...

I would expect most accountants are pretty reasonable in this area. The most important part is having the information so it is easy for them $. ie contract notes .

The tax office to my understanding has access to most of this information now and maybe even acceptable for your accountant
to gain access to it with your knowledge?

I know they were working heavily in this area a couple of years ago according to the money doctor i use . So if you don't have long trades from many years ago it maybe relatively easy for them if you have no stored capital losses.

The easier you make it the cheaper it is ! ie buy sell contract notes in order . brokerage rates etc.

Good on you for getting the house in order early as this is what will help them determine the closing value if needed and yourself if you need rebalance.