I believe the thank you was regarding the mod-friendly mindset of early valve. A section in the game menu for loading new mods and it shipped with a mod (TFC, which was based off a community mod for Quake)
I don’t know about the launch release, but the Game Of The Year release is the one that shipped with TFC, plus (what we now know as) the GoldSrc SDK was on the disc. Every tool they’d made they used to build Half Life, they put on the disc and gave to customers.
Fucking legends.
So many great games and mods came out of this… Counterstrike, Day of Defeat, Sven Coop, They Hunger. The amount of hours of gameplay for the price of a single game is unbeatable. Many people started their careers as Half-Life modders.
I believe you are right as well, my friend had the game new and I think the SDK was there, but not TFC.