In this case: Because you told me that the second transaction is also yours, the second transaction spends that output again, and, hence, you – or rather your wallet app – must have had the key to spend from it, it must have been your address.
For Ae2tdPwUPEYwWg3FJkm1xw1rh7W7vAstZb3QaZkM73FwLiZYvSWuKYQxjne, it’s not that 100%. You haven’t given a transaction where those 3515.512963 ADA are spent again. So, it would be theoretically possible – but highly unlikely – that it is not your address. Since it gets the much larger and much more crooked sum, and since it is also an
Ae2… address like the other addresses from your wallet (presumably a Yoroi wallet), it is most likely a third address of your wallet.
(Edit: Scratch that! I just saw that that is your first address again. I actually can’t understand that. It shouldn’t have happened in Yoroi – except if there was a bug back in 2019. It really wants to use new addresses all the time. Which wallet app(s) did you use?)
Yoroi did use new addresses for the change every time. And it also gave you new, unused addresses to give out to receive ADA from others every time it saw the last address being used. So your wallet consists of lots and lots of addresses. Yoroi still does that, but nowadays those are Shelley addresses – looking like
addr1… and not like
A lot of wallet apps now use a single address forever, since it doesn’t make any sense for privacy anymore, since the addresses are linked by the common stake key contained in them, anyway. It is not a must of the UTxO model that there have to be that many addresses. There can also be a lot of UTxOs on the same address. You can see that in your first transaction, where two outputs from the same address are taken as inputs.
But accounting software, explorers, wallet apps, still have to know how to deal with the history of those multi-address wallets if they are not totally sure that they will only ever encounter single-address mode wallets.
I can’t completely parse that. There cannot be two transactions sharing the same hash. It is still one transaction, but it can have an arbitrary number of inputs and outputs.
Existing tax software should, in fact, already have logic to deal with the UTxO model, since Bitcoin uses it. In Bitcoin, you also have these lots and lots of addresses all belonging to the same wallet that have to somehow be consolidated in accounting and tax reporting.
And accounting also should have no problem dealing with transactions with multiple in- and outputs. It also happens in real-world transactions, not only in crypto, for example, when value-added tax has to be separated from the net revenue, or when a transaction contains fees.
Haven’t done my taxes up to now, but I would want a tax software that can consolidate addresses into accounts and further all of my accounts into a grand total of my holdings. Tax authorities might want to have the address-specific information to validate/verify what you are telling them (or they might not bother), but in the end they are probably not that interested in the technical details of wallets and addresses, but just in your overall profits. But it’s best to ask them what they want … or look if they already have how-tos online.