You can tear it down to look, it aint that complicated. Just be sure to have the right screw drivers that fit. You don't want to scratch it up. I once owned its mate. Think mine was made in 1906. Might as well clean and re oil it when you have it apart.
First I like your dog!!
You have a nice colt that looks original to me.
The Eagleless grips are correct for the year. The patent dates or correct as being 2-line. The 7 in the hammer slot is a good inspector's mark for that serial number. I think I see the trademark on the left side. It should be a rampant colt in a circle. If the base pin has a hole in the end it is correct for that year. The serial number dates it to 1900. You did good.
Those second set of pictures show the gun better than your first picture. It looks like that gun wasn't used or abused much. It`s worth more than I first thought with your first post. The grips doesn't show much handling.
"It's amazing what people will believe on the internet so long as it confirms their preconceived notions."
I think so. They are expensive and a long wait. Really a gamble but it would show where it was shipped and when and in what configuration. If yours is unmolested it would certainly help. Dang the price though.
You can pretty well tell the gun is "unmolested" from your photos. The biggest issue with these old SAA are cut down barrels which are fairly common but they do affect price. Your barrel is the original 4 3/4" length as evidenced by the two line address on top of the barrel. I see case colors and blue. I see the large dished ejector head. Everything looks fine to me. The base pin is a minor item and I wouldn't be concerned with it being right or wrong as long as it is a Colt SAA pin which it is. The money for a Colt letter will give you a shipping destination which could really help it if shipped to an individual, Mexico, Southwest USA or any other romantic destination. If Eastern/Midwest shipped to a sporting goods store or hardware store then the letter will not help it much. Everything else the letter will tell you, you have already learned on this forum. It is a nice gun and worth the $2K spent even if it was not a "steal". Hope this helps.
Many of those vintage of SAA's had interesting shipping destinations. Worth a shot.
'This is King Fisher's Road--Take the other one'