There's an allegation running around that Tesla vehicles deliberately overstate mileage driven by an enormous amount -- as much as 30%.

If true this is yet more evidence of the utter insanity of not demanding -- and enforcing by whatever means are necessary -- that laws be actually enforced evenly and against all no matter who it might be.

Federal Statute in the form of 49 USC Chapter 327 governs this and is uniform throughout the United States. There is also a regulation regarding the allowable deviation ("error") in said odometers, which is reasonable because tire size can differ somewhat and (particularly mechanically) ratios may not be exact -- the standard, set by SAE, allows a 4% error although this is actually not codified anywhere I can find in either statute or the CFRs.  Thus anything less is going to be considered reasonable and allowable error -- five to seven times that much is not.

Some small degree of error is expected over time; a new tire, for example, typically has 11/32" of tread and at 2/32" its legally worn out (to the bars) although I almost-always replace them at about double that as handling, especially when wet, gets squirrely around there. So there's roughly 1/2" of diameter difference between "new" and "worn out"; a typical "car" tire might have a diameter of ~32" so there's a roughly 1-1/2% difference in the odometer reading between "new" and "fully worn out" tires of that size.  However, either mechanical coupling or an optical encoder as is typically used in modern vehicles is extremely repeatable.

A car rental company was, a number of years ago (20ish) was convicted of fraud for putting one-size smaller tires on their fleet resulting in overstatement of mileage driven by about 4%.  They got hammered for doing that so I would presume an intentional error wildly greater than this could be serious trouble.

Designing and selling vehicles that intentionally overstate miles driven would be a wild-eyed intentional act.

I find it difficult to believe that Tesla and Musk would have put millions of vehicles onto the road with inaccurate odometers, all biased one way (which means its not a mistake) on purpose and all of which will screw a lessor as they will be charged for miles not actually driven, also screw customers on warranty coverage as mileage is part of the limitation on warranties and at the same time produce an overstatement of driving range on a charge.

I will note that the maximum civil penalty for odometer fraud is $1 million, which is peanuts in any large corporation's pocketbook.  However, that same statute provides for felony criminal penalties and that would not be the limit of it either because fraud is not limited in that fashion and anyone who got screwed on a lease (mileage overage charges), had a warranty repair denied due to mileage that was somewhat over the limit and anyone living in a locale that charges EV owners a mileage-based tax (because they do not pay fuel taxes since they buy no fuel) all have claims and all of them would potentially be subject to treble damages as actually designing to this standard isn't an "accident" or "optional"; it is in fact required to sell cars in the United States.  I would bet that any "standard" arbitration clause would be tossed instantly by a court on a fraud allegation -- that should be able to toss it because if the contract was entered into under fraudulent pretense then it never occurred and the clause is invalid.  This will be interesting if someone litigates that and Tesla tries to have it tossed back into arbitration.

In addition this makes any such vehicle where the seller has reason to know the mileage is not actual must check the "mileage not actual" box on the title when the car is sold.  This would be very likely to have severe impacts on the market value of such a vehicle -- it sure does for any other car!

Again I find it difficult to believe that Tesla would have done this -- but there are in fact reports of it being an issue going back several years.  I'd be happy to clock anyone who has one near me (NE Tennessee); I've got my Mazda which reads the trip meter in tenths and I also have a GPS, of course, which can record trip distance in my phone.

How about a nice test across oh, say, 10 miles up the highway, we measure from actual mile markers on the road and then we pull off and compare notes, take photos of each other's odometers and trip meters (if its only in one of them rather than both) and present the evidence?

I can go pace out such a run that ends in a Rest Area right near here -- which makes the "pull off the road" part easy, and the start then would be from a freeway entry ramp, allowing easy zeroing and recording of the starting mileage.  Further, I can pace it with at least two (and maybe four or five!) different vehicles prior to the public and imaged test, all with vehicles that read to the closest tenth, so qualifying it as repeatable will be easy.

Let's test this and put the question to bed quite publicly; if the allegation is false then what's circulating around is bullshit, but if its true then it needs extremely wide exposure and Tesla must be forced to both fix it and compensate everyone who got fucked.