Hey Jake, I found you via the steam page and I am really super excited for this full release. I've just recorded a playthrough which I'm currently editing and should be up within the next week.
I may not be a 90's kid, but all my siblings are and I grew up on this stuff. Monkey Island, Grim Fandango, Indiana Jones, Day of the Tentacle, and that one about the drillers in space (lol).
Anyway, I may be in the wrong here and have it backwards, but I belive the steam version is older than the current Itch.Io version. Either this or there's a bug on the steam version where the letter can't be opened as the "look" function is unavailable when the inventory is open.
Can't wait for the full release!!!