Back then there was no early access or dlc so companies had to make a full game polished and ready on release day 1. I think older games are better because of that.
Let's just state that there were released at least three versions of the original Space Invader, since the early ones were bugged.
You can "finish" Pacman if you get the maximum score possible. After that the screen becomes a mess and you can't see anything anymore (even if you can play blind then, but if you get there you can play the game blindfolded anyway)
Even if the old games were a LOT simplier than the modern games, they were not bug free.
Did you notice that most Sierra adventures on GOG have a folder of files that are named "patch" or something similar?
Missing rooms, graphic files, bad scripts ... yes, you would need patches for that.
The games of the late 80s and early 90s DID have bugs, but we learned to live with them. In the rare case that a updated was released, you would contact the publisher, send in your discs (I'm a Amiga child) and get new ones.
Also - in case of DOS games - game magazines would include patches on their cover disc on a regular base.
I think it was CD 3 of Gabriel Knight 2 that had to be sent back in for a bug fix.
Since almost every game was bound to run on a specific hardware (Sega, Amiga, PS, you name it), it was quite easy to avoid bugs with drivers or exotic hardware configurations. The worst that could happen was that someone put a Zorro accelerator to his Amiga or some exotic Headset to his Sega console and the game would not run. Solution? Unplug the exotic hardware.
Let's forward again to the late 90s. 3D acceleration for Tomb Rider. No bugs with Matrox or S3 Virge, since they simply were not supported at all. The only accelerator supported was the 3Dfx Voodoo and you needed to download a special .exe for it.
We blamed the hardware much more than the software at that time. Today we expect the software to run no matter what our computer is made of. Some don't even accept that a game requires the newest Windows10 version.
What Steam changed (and let's face it, the credit goes to Valve), was the way, patches were distributed. Before it, we would visit the publisher ftp server on a regular base to look for patches.
Two fun facts:
A BIOS update to my graphic chip in 1998? I got sent a new chip via post office and then returned the old one.
The DVD Version of Lego Star Wars 2 could not even be installed, the disc was labeled wrong and the installer did not recognize it. LucasArts of course offered a fixed installer to download via ftp, but many parents who had no idea about computers returned the game to the shop.
No, the software in the "golden" days did have just as many flaws as modern software. It was just handled in a different way. Yes, back then it cost the publisher more to get a fix out, that's for sure, but on the other hand it cost him a LOT less to test the software, due to the limited hardware variations.
edited, corrected game name