I have no doubt that you are all correct that any dogmatic use of Donald's numbering is risky. I suspect that this may be down to a variety of issues. One is the holding back of consecutive numbers for a pair that might be ordered at a later date. Also the delay between the order and delivery and the construction of guns for 'stock' may have messed up the numbering.
Since my dating interest as a importer to the US is in the antique status of guns, I use the early numbering blocks as a negative rather than a positive indicator of age ie if it is numbered higher than 16000 it is very likely post 1898.
The only way to be certain is to request the record from H&H who I have always found to be extremely helpful and efficient.
