It does matter, contrary to your assertion. The information on the W-9 is what the requester will use to complete the Form 1099-MISC, and as you note that form does matter. If the requester doesn't get the 1099 right there is the potential that the requester gets fined for failing to file the 1099 as required. While the requester can rely on the information given so long as the requester has no reason to believe it is wrong, it is still a headache for the requester to have to respond to the IRS over 1099 errors. So the requester very much has an interest in wanting that information correct, i.e. the Form W-9 information does matter. If it didn't matter, the IRS wouldn't have bothered making a form for it.
Well, the Form 1099 instructions make it crystal clear what the issuer is supposed to put on the form.
your social security number (SSN), individual taxpayer identification number (ITIN), adoption taxpayer identification number (ATIN), or employer identification number (EIN)
Like I said, it's anybody's guess if they put down the SSN or EIN if he gives them both. They might take his EIN off his new info he sends them or look in their old documents and use that #. Same goes for the name.
The 1040 return has that information, yes. The problem for the IRS is also ensuring that the 1099 accurately matches that 1040 return. If the entity date — Name and TIN — don't match that is a problem. You seem to be assuming that as long as the EIN is right it's all good, but that's now how the IRS processes returns. It looks for both the name and TIN to match.
Unless you're a programmer who works for the IRS or someone involved with the matter, there's no way for you to know exactly how the IRS handles such matters. If OP is really interested, he needs to request a transcript and match up what's in there to his collection of 1099s.
However, given that some 1099s are handwritten and given that business names can easily have their names misspelled (LLC vs L.L.C.), I'm betting in practice the IRS enters the EIN/SSN first and sees if the name is at least close to what's on the SS-4, 1040, or Sch C and goes from there if there's a mismatch initiially.
The requirement is that ALL income must be reported on the return, whether a Form 1099-MISC is issued for it or not.
I'm strictly talking about their computer matching system, which checks if he reported
at least as much as the sum of 1099-MISCs issued to his EIN/SSN.
Should you get audited and the IRS determines that you did not report all the income you are likely to get hit with, at a minimum, a penalty for negligence, which is 20% of the underreported tax, along with the tax and interest, too, of course. And if the IRS believes that the underreporting was intentional, it can be much worse. The IRS could apply a 75% fraud penalty and/or pursue criminal prosecution.
"At minimum," if he gets caught, he'll get a computer-generated notice saying he failed to report $1,000 or however much in Sch C income (if his 1099-MISC sum is > his Sch C gross income) and have to pay a little interest as well as additional tax due. Sometimes they'll attach a small penalty, but those can be abated. Anything beyond that is fleetingly unlikely/almost impossible unless he's hiding millions in income.
So the IRS is not "OK" with just reporting at least as much as the 1099s show. Doing that will prevent getting an automatic letter from the service center, but it certainly isn't good enough to meet the legal obligation of reporting all your income.
Again, we're talking strictly about the computer system.