I do not know what information actually transmits to the ATO using Etax but I would be very surprised if more than the totals actually transmit through
Using tax agents ELS (electronic lodgment sytem) all the various schedules are used to complete capital gains schedules, dividend, interest and so on using the various software but it is only the final total that is actually transmitted to the ATO
And yes the ATO is accessing information from share registers, title offices and so on to match against capital gains declared but they are only match totals in tax returns against seperate pieces of information gained from various sources.
As for the tax return being 100 pages long if you included every transaction seperately. If you have that many transactions in one year you would have a hard case to argue that you are a share investor and not a trader and as a trader you do not show the transactions a capital.
