Model 1893 trigger plate

[MikeJordan]

What year, and why did Marlin add the hole on the trigger plate for the lengthened carrier?

[marlinman93]

The extra hole and screw for the left side of the trigger plate was to better support the trigger plate. The length of the carriers didn't change from the very first 1893 forward. The extra screw was added about the same time the smokeless powders and high pressure loads became common. No exact date, but I've seen the extra screw on guns lower than 170,000 which is the pre antique era by ATF regs.
My 1893 takedown is in the 124,000 range (1895) and doesn't have it. But another 1893 I own is in the 140,000 range (1896) and does have it. So I'd guess in the year 1896 is probably as close as I could assume.