Cleaning is good, but you don't want to soften it. So nix the saddle soap or Gloveoleum. If you over-soften it, it will lose it's rigidity and just turn into a big sloppy mess. I just use glycerin soap and warm water with a soft brush. Just look for a soap marked "glycerin" at the supermarket. It's not hard to find. The more natural glycerin soap the better so you might want to hit a Whole Foods or something. But I've found it at Kroger. Or buy somebody's fancy holster cleaner.
The reason I remember 549 is (5-4 =1) then the 9 = 19. I used to fill out orders to Lawrence for customers when I worked at a large gun store in a past life. I did several a week. I had that exact holster. Except mine was basketweave with the sight protector ("BS").
Where I was, full-flap holsters were popular because of the protection they offered in the field. While a Model 19 was $200 or so, that was a lot of money at the time. Guys wanted to protect it.
Time frame is hard to nail down, but it's not one of the pre-made ones that came later on. Pictures would be nice. Originally they were all made to order and marked as yours is. At some point they started making them in bags for point-of-sale displays. Yours is most likely an ordered one. The pre-made ones were mostly marked for the gun..like "6 1/2 BH" for a Blackhawk, or HS for High Standard, SA for Single Action Army, rather than codes. They had a different name for the "line" they used for the point of sale holsters but it escapes me at the moment. It was just on the packaging, which was a Ziplock bag rather than the box the ordered ones were shipped in.
The Model 14 came without the snap installed, and with instructions on how to install it to fit your gun depending on what kind of grip you had on it. Targets, Magnas, Herretts, Ropers, whatever.