I don't know what NaN means; but with $1918 for coach-coach-coach and $1142 for coach-BC-coach, one of them mustn't be real.
Possibly this is greatly simplifying the definition, but it would seem that when working with Excel, an entry that returns something like "DIV!=0", is a NaN.
But more to the point at hand is that even airlines, with their demand pricing far more perfected than Amtrak could ever expect theirs to be, also have their "moments". There are documented cases where an airline's own site has unintentionally quoted a $1 fare for a flight. The airline is stuck, as existing regulations require they honor such (not sure if a third-party site were to quote something like that).
I've had cases of such myself - and I'm only an occasional flier (YTD: 2 flights; 2 more booked). During '16, a posted fare to Munich on United was $4500 - and that involved connections. This was a "take it or leave it"; I wanted to go so I reluctantly took it (only other on the route is Lufthansa; they and United code share, so their fares will be in "lock step"). But I still periodically checked their site. I couldn't believe it when a $2500 fare showed up - and this was on Nonstops. Hey, for that diff I'll take the $450 exchange fee and rebook - and make it my business to use the $1500 voucher before it expired a year later. This could well have been a "mistake fare", as a day later, it was gone.
Now this year, it was more of same even if not quite as dramatic. For a round trip to Munich (the draw for me is the Salzburg Festival), the fare I first see again is $4900 on both of 'em. I said unacceptable and just wasn't going to go (I go to concerts to hear works I haven't heard before; and at Salzburg there is a lot of "play it again Wolfie"). But "just keep checking" and a $3200 fare showed up. That was acceptable and I grabbed it. It lasted for a week and is now gone.
I wonder why the airlines are now seeking relief from the DOT (their non-Safety regulators) from both "mistake fares" and from the prevailing 24 hour rule allowing a no penalty CX.
Maybe Amtrak posts these "mistake fares" and maybe they are obliged to honor them. I defer to those (most all around here) who ride Amtrak more frequently than do I (I'm pretty much a "once a year" on Auto-Train).