-Indy 1978, and then the Stage 7 which moved the holes to the new closer together configuration that we use now in 1993
I think Venture were the first to actually have six hole baseplates, closely followed by other brands, but yes around 1993 is the first year more commonly credited with the change. When you think about it, Ermico was the place in SF where Indy, Thunder and Venture were all being made, so I think as soon as one truck brand got six hole baseplates, the others would follow soon enough.
Prior to that people were drilling in their boards and trucks from 1990 I think someone had said in an interview about it, when being able to slide on the ends of your board became very popular, but as with anything from way back then, I don't think there was any one specific person or place that it was happening first, but just more due to the evolution of skateboarding and people trying different tricks all over the place.
Always funny what AI searches come up with these days:
Independent Truck Co. is widely recognized as the company that popularized the standard 6-hole baseplate design.
While skaters were drilling custom holes in the late 1980s to prevent hardware damage, Independent cemented this design in the early 1990s (around 1992-1993) to allow for both "old school" and "new school" mounting patterns, a feature that persists in their 159, 169 and 215 models.
Key Details on the Development:
The Trendsetter: Venture Trucks is also cited in some historical accounts, with Greg Carroll claiming to have been the first to make the 6-hole change in 1992 to accommodate ledge skating and prevent hardware damage.
The Evolution: Independent moved to a 6-hole baseplate during their Stage VII (1993) era to reduce bolt wear.
Purpose: The 6-hole design was introduced to allow skaters to switch between old-school (further apart) and new-school (closer together) mounting patterns on their decks.
* I am sure there was a better one of different truck baseplates, but this is a good one too:
https://www.instagram.com/kristiansvitak/p/CztO3I1uZb9/