My early guns with One-piece ivory grips:
#1046 38x3-1/2" Nickel, Colt letter says SNL, shipped 5/24/77.
#2191 41x6" Nickel, No Eject, Colt letter says Ivory, shipped 10/4/77.
#3527 41x6" Nickel, No Eject, Colt letter says Ivory, shipped 7/3/79.
#6490 41x5", Nickel, W/Eject, Colt letter not requested.
#6599 41x5", Nickel, Engraved, W/Eject, Colt letter says Ivory, shipped 5/9/78.
Also, based on the first 21 years of production (39547 guns sampled) 939 had factory recorded ivory grips (slightly over 2%). Total prod at end of 1897 was 107,500.
One final statistic; During 1877-79, 380 Colt M1877 DA's had Ivory out of 19,000 produced guns (Oh, and look at that! 2% Again).