Plastic kit manufacturers have a long history of screwups regarding the scales of sailing ship kits. I long ago reached the point where I quit paying attention to the scales listed on the boxes.
I haven't actually measured the old (1956) Revell kit, but I think the scale of it is in fact 1/192. That's how it's listed in Dr. Graham's fine book, Remembering Revell Model Kits (which, admittedly, lists some questionable scales for other sailing ship kits). 1/192 is the equivalent of 1/16"=1', which is a fairly standard ship modeling scale. This kit was Revell's very first sailing ship; my theory (for which I have no hard evidence whatsoever) is that the designers deliberately chose that scale for the kit and designed a box to fit it - thereby, perhaps inadvertently, starting the infamous "make-the-model-fit-the-box" policy when they released the next two kits in the series, the Bounty and the Santa Maria. (I know for a fact that the Bounty is on the oddball scale of 1/110. Dr. Graham says the Santa Maria is 1/90 - but the crew figures in those two kits quite obviously are on the same scale. One can quickly get a headache trying to sort all this stuff out.)
The Monogram kit with the one-piece hull was originally issued long before the company merged with Revell. Those two companies were semi-vicious competitors for quite a long time. (In Dr. Graham's book about the history of Monogram he tells an interesting story of two 1/48-scale B-17 kits. Revell's B-17F appeared shortly after Monogram's B-17G. Most parts from the two are interchangeable - down to the locator pins and holes - except that the Revell parts are very slightly smaller. Styrene shrinks slightly as it cools; it was perfectly obvious that Revell had based its kit on Monogram parts. According to Dr. Graham, one of Monogram's executives wrote one of Revell's executives a very nasty letter, but chose not to take legal action.)
Back in the late 1920s, when the Constitution was undergoing restoration prior to being put on public exhibition, the Navy published a set of plans for her. Those drawings were based more-or-less on her then-current configuration - including the raised bulwarks, the relatively narrow main hatch, etc. I think the designers of the 1956 Revell kit based it on those plans, with one big exception: for some reason or other they got interested in the Andrew Jackson figurehead, and created a beautiful miniature version of it to replace the simple billet head the ship actually had at the time. It's unlikely that the real ship ever looked exactly like that; she almost certainly didn't during her years of active service. The naval officers who made the decisions regarding the restoration weren't professional historians, and they made some judgment calls that would be regarded as near-heretical today. (For example: they found several different sets of spar dimensions from various dates in the ship's career. So they averaged all of them and had a new set of spars built accordingly.)
The Anatomy of the Ship volume has taken some pretty brutal criticism in a number of quarters. My opinion of it isn't as low as some people's, but I have to say I find it disappointing in a number of respects. The author apparently didn't spend much (if any) time examining the actual ship, and he missed several important sources of information (most notably, perhaps, the old "Isaac Hull Model" in Salem). One example of the book's weaknesses: the framing plan on pages 60 and 61 is pure nonsense. There are a number of good, clear (and easily accessible) photos of the ship's hull with the planking stripped off; they show that her frames just plain weren't arranged like that. I really like some of the drawings in that book (the reconstructions of the transom, for instance), but when it comes to such things as hatch dimensions I'm not inclined to trust it.
There are two other good sources of Constitution plans - both of them reconstructions of her War of 1812 configuration. The first is the set George Campbell drew for the Smithsonian in (I think) either the late fifties or the early sixties. That set was the basis of the 1/96-scale Revell kit (and the smaller, "quick-build" version that was based on it). I've heard some vague criticisms of these drawings, but I'm not aware of any major, indisputable errors in them. The other set is the one published by Bluejacket Shipcrafters. The individual responsible for it was not a draftsman of Mr. Campbell's training or experience, but he made the project a labor of love and spent an enormous amount of time on it. (He also, as I understand it, consulted extensively with Capt. Tyrone Martin, one-time commanding officer of the ship and probably the reigning expert on just about every aspect of her. Captain Martin's book is conspicuously absent from the bibliography of the Anatomy of the Ship volume.)
It seems remarkable that the details of such a famous ship - and such a popular model subject - are still so hard to pin down. But such seems to be the case - and I suspect it will be for the foreseeable future. I continue to hope that, in view of the critical reception the Anatomy book received, Conway will publish a revised and corrected edition of it some day. But even if that happens I suspect the results won't be accepted as "definitive."