Yes, within the context of the type of sites I was discussing. You already indicated that you know that they are not actively maintained. Knowing that, it doesn't really matter if a breakage happens every year, 3 years, 5 years. There's no point at which it becomes "OK", if you believe in the long time preservation of content.

I'm not picking on maps specifically. It's a compounding effect of many individual parts slowly breaking. I would even agree that you did a reasonable job of maintaining backwards compatibility, but that doesn't matter...broken is broken. Content gone is content gone.