I've been using Sebastian Bold and other versions for recreational projects, and I've noticed that in the 70s, there was a version with different letters, and I've cone here to see if there's an available download for it. I've tried matcherators, but they only tell me the version I have. Here's a picture of the alternate letters, and what it looks like in the font I have as a reference. Thanks in advance to anyone with a response.

Buenas!!, Pues mira me tomé el Tiempo de Buscar en todas las Web de Fonts, y en Ninguna encontré la font. También la busqué por las opciones de Imágenes pero tampoco nada. Probablemente la font haya sido modificada para esa Pelicula, Canción o Libro que tu vistes. Lamento no haberte podido ayudar!! :(

I don't think a version that includes those alternate characters was ever digitized. Have a look here:

https://www.dafont.com/forum/read/154765/what-is-this-font

many people are looking for it:
https://old.reddit.com/r/fonts/comments/10w6vv5/anyone_know_where_to_download_serif_gothic_with/
https://old.reddit.com/r/fonts/comments/dpq3ft/is_itc_serif_gothic_with_alternate_characters/
https://old.reddit.com/r/typography/comments/t7l08m/has_anyone_ever_made_an_opentype_version_of_itc/
...


Here's the page 178 of "The World-Famous Photo Typositor Alphabet Library" (1973) by VGC (Visual Graphics Corporation)
https://archive.org/details/worldfamousphoto0000vari