they dont have your deduction information though, also for investments they dont always have cost basis info. other than that for simple returns they can absolutely do an automated federal 'tax receipt' with standard deductions.
> they dont have your deduction information though
Except for medical bills, mortgage deduction, education expenses, retirement/HSA/etc. accounts and SALT (if that gets reinstated) and maybe a couple of others, probably. Although, frankly, I'm not sure what deductions other than charitable contributions don't get reported to the IRS and I'm similarly not sure what deductible expenses don't already have a paper trail I would care about retaining. But that's where "correcting the math" would include replacing the standard deductions with itemization would come in.
I think requiring a basis for investment income to be made in the acquired year to the IRS is both reasonable and trivial.