Harold Jenkins would be the guy to ask. He's worked on a lot of the Brantly's at one time or another. A lot of aircraft that are wrecked or scrapped will remain on the databases. People just don't bother changing their status. Many of those you may find are just a logbook and a dataplate. That's one thing to look for when you go shopping for an aircraft. Just because it's advertised as a newer aircraft may not mean much. If it's a rebuild, it may have a bunch of parts from an older aircraft so only the airframe may be new. Now that's not necessarily a bad thing if the parts are low time and have traceability. Then again it may be an older aircraft with a dataplate off a newer machine. Unscrupulous sellers have been know to do things like that.

A careful look at the logbooks will tell the tale. I've rebuilt a few helicopters over the years and have seen it all. I'm sure you know but a careful pre-buy by someone knowledgeable about the machine is mandatory!!! Don't get suckered into using the seller's mechanic either
Don't be scared off by an older machine either. A lot of these Brantly's have very low hours on them and if you can find one with most of it's original parts that's been maintained well, it could be a good deal.
I think you'll find the TBO on the Brantly engine is due to the lack of data on these engines. What I mean is that there are just not enough engines that have flown enough hours for Lycoming to determine if a TBO extension is warranted. I would imagine someday it might be extended to 1200 or 1500 hours like the Schweizer's. I highly doubt it will ever become 2200 like the CB's or R22's due to the fact that it just works too hard. You would have to have a more powerful engine derated to be able to get to that kind of TBO.
Now, as to the fact that most of these engines never reach TBO. I suspect what you will find is that a lot of these machines just do not fly that much. That's the worst thing you could ever do to an engine. Especially one that works so hard. Any degradation in performance will be immediately noticed, hence so many top overhauls. Back when we ran Hughes 269's, we often operated them right at max power in training scenarios all day long. We regularly ran them 300-500 hours over TBO. Most of the private owners never even made TBO. They averaged maybe 100 hours a year, we were averaging 600-1000 hours per year. That along with mandatory 2 minute cool downs and regular oil changes really made the difference. We ran iridium plugs too. They'd make TBO as well and in all those years I only had one plug fail. They'd be full of oil and still fire! Just the thing you want when you need all the power you can get.

Those little Lycomings are real beefy. Remember, just because you are running near max RPM doesn't necessarily mean you are at max power. True, in the Brantly you are going to be asking a lot but once you get moving and up into cruise you are going to be operating at reduced power. Unless you are planning to be doing mostly hovering at high gross weight you may not be so hard on the engine as you might think.