Model 1875 "Types"?

[Jay Huber]

I have never heard that but perhaps they are referring to the first guns had a Pinched front sight and the later models had a Blade front sight Jay Huber RSA

[oldremguy]

There is a excellent article on Variations in Remington Model 1875, Model 1888 and model 1890 revolvers, by Don Ware in the 1st Quarter 2004 Remington Society of America Journal.
Hope it helps.