IRS e-file software would not have to pre-fill every source of data they have, making them vulnerable to fraud if a taxpayer notices some income wasn't reported

IRS e-file software would not have to pre-fill every source of data they have, making them vulnerable to fraud if a taxpayer notices some income wasn't reported and realizes they can get away with "forgetting" to report it. All they need to do is offer free e-file software and fill in W-2, 1099, and any other standard information that everyone knows is going to be reported anyway because it comes from employers or financial institutions. IRS could still leave it up to individuals to self-report any other sources of income, even income the IRS knows about through other data sources. They don't have to show all their cards. Other countries already have systems like this. How do they handle it? Do they tell taxpayers what their tax bill is based on all data sources, or just the standard ones (incorporated employers, financial institutions) and expect taxpayers to fill in the rest even if the government already knows about them? I think it's more a theoretical problem than an actual problem. Getting away with not reporting income at the time of filing because the government doesn't know about it sounds fun, until the government discovers that income later through updated or alternate sources, and then you have to pay that plus penalties. Betting that the government won't know about it ever because they don't know about it now seems like a bad strategy. Any income the government very likely doesn't know about, like cash transactions, is already reported on the honor system, and only because of personal ethics or fear of audits or employees whistle-blowing on their employers' tax fraud. None of that would change.