Importing from Gamebryo 1.x, but get: NifError non-zero block tag <number> at <offset>

[neonrust]

Backstory time!
I'm trying to rescue data from a game I was involved in the development of, back in 2003.
I'm not entirely sure what version of Gamebryo was used, maybe 1.0 or 1.1. I do remember it was shortly after the name change from NetImmerse.

Anyway, A bit after it was released, catastrophe struck: our git repository server (holding all the source & assets) had a fatal disk crash. Of course, being total n00bs, we only used the background radiation of the universe as backup... (i.e. none)

It was all thought to be lost until a few years ago a git clone was discovered on an old machine. This clone was from a programmer machine so it unfortunately only had the exported nifs (and textures), not the actual source assets (and the c++ sources of course). We exported the nifs from Maya, with an official plugin, I believe?

I did ponder contacting the publisher for a bit; they did receive copies of the source, after all. However, considering that company no longer exists, and has even been engulfed by other companies, several times, I think that would be a time-consuming (and fruitless) exercise.

This endeavour it completely my own initiative, there's no business case or anything like that. There's only sentimental value. :)

End of backstory!

When importing any of the "room" nif files I get this error:

At this point, I'll take what I cat get out of these files. If I could get the vertices and face information I'd be thrilled.
Is there a way to "ignore" unknown stuff?
Or is there some pre-processing that can be made, like hex-editing? ;)