The locomotive order sheets were also done by hand, which sometimes led to its own problems. Handwriting wasn't always perfect. I believe one of the SRRL 2-6-2's was ordered with an 86 inch wide tender, but Baldwin mistakenly delivered it with an 8 foot 6 wide tender that proved rather tippy. Obviously someone goofed reading the order sheet.
The spec sheets I've seen from Mason usually have somewhat worse handwriting than those from Porter or Baldwin, at least to my eyes. When I read above that the H&TL engine was delivered to the wrong gauge, I immediately wondered if it had been intended to be standard gauge (4 foot 9) and instead built to 49 inch. That doesn't seem to be the case though; it appears this particular road was always meant to use some strange gauge.
As for gauge standardization: This is the 1870's, the height of gauge experimentation. What we now call standard gauge (either 56.5 or 57 inch) is the most common, however many other gauges exist. There are various narrow gauges, 2 foot, 30 inch, 3 foot, 3 foot 6, 4 foot gauge, etc. Then you have various wide gauges like 6 foot gauge and 5 foot "southern" gauge. Some 4 foot 10 ohio gauge may still have been in use, I'm not really sure. If an odd gauge was chosen for an isolated railroad, it was most likely because it seemed like a good idea at the time to the engineer who was planning it. The big push to a national standard gauge happened mainly during the 1880's and 90's--most the narrow gauges widened, and most the wide gauges narrowed.