As I understand the law, it is unrelated to the sale platform or the sale process - it is related to your individual record-keeping. ie if you record (eg in your own spreadsheet summary) that your sale on date Z is of parcel X bought on Y date then that is what holds for your tax purposes (of course you do need to have a complete set of records of similar form). ie You can choose what parcel has been sold if and only if you keep that record.
Of course, this is not advice to you for investment or tax purposes, so ask your accountant (and please post outcome of that advice if different).
