It would be interesting to see which is the real 5510. I would think that since one of them was at Knotts that it was probably the real deal since it would have received some care, while all of those out on the farms get pretty neglected.
Looking at the numbers sure does get difficult. Out of the 160ish 3000 series boxcars my father and I looked at, I'd say at least 30% we couldn't ID for one reason or another. And then when you get into exterior paint, that becomes even more interesting... on the outfit car we purchased, we couldn't see a number until recently. We were there at the right time of day and could make out the 04946, but before, we couldn't see it because of the lighting. In general, we tried to be pretty conservative when numbers were in question, and so far, we've had no duplicate car numbers.
By the way Vic, one thing that I've wondered about was the fact that your lists had 5549 in the Helfin site and the Honeycutt site. I know that the Friends got the car from the Helfin collection, and unfortunately, the Honeycutt collection is all gone (I could kick myself for not investigating back in 2000 when they were still there, especially since you say they were such nice people). Do you still have any notes that might indicate what the "5549" in the Honeycutt collection might also have been?
There is always the chance that car numbers got switched. A list I received from someone on this board of their cataloguing of equipment in 1970 showed some interesting finds on the D&RGW system, including some flats with 3000 series numbers...where there was also a box with the same number!
I still cherish my copy of your book. A lot of time and effort for such a great work.