I finally solved the issue. It only took me years!
So if you still want to play Sierra CoCo3 games, follow these steps:
1) Use VCC and the dumps of the original disks. Newer versions won't do.
2) Load the disks with the instruction
DOS, then you will be prompted for the date and time of the system. Use the same syntax as you're given.
3) Then, load the games with the
SIERRA command.
Now you can enjoy said games. Thanks to those online kindred souls that helped or tried to.
