Some 1997, all 1998 transmissions "beefed up"?

[Danno]

According to Wikipedia (so it must be true), "Some of the internal components of the 4R70W automatic transmission were reinforced for greater durability and reliability in late 1997 models and all 1998 models."

I'm looking at a 1997 LSC right now, does anybody know when in 1997 the beefier transmissions started happening?

Apologies if there's a thread on this already, my searches proved fruitless. Thanks.