Should "standard errata" be applied to silver-bordered cards?
One of the wonderful things about silver-bordered cards is that we can do stuff that maybe doesn't technically work but that players would have lots of fun trying to make work.
  
  &mdash;Mark Rosewater


In other words, the Un-sets were never designed to perfectly follow the rules of Magic. That's probably a big part of why they don't bother giving them rulings and errata in Gatherer.

So, what should you do? It sorta depends on what your goals are.

Serious casual play: play 'em like any old cards

How do people play old cards without looking up Oracle rulings all the time?

Well, if you get familiar enough with the comp rules and the general shape of Oracle errata, you don't really need to most of the time. Sure, I might need to look up the rules for Chains of Mephistopheles every time, but I can just look at most cards in Legends and know what they're trying to do, even if the words are all backwards and the text is terrible inconsistent about "sacrifice" vs. "destroy" vs. "bury."

You can apply the same approach to your Unglued/Unhinged cards. What does "cards in play" mean? It's clearly old-Magic language for either "permanents" or maybe "non-token permanents." When someone proposes a crazy nonsense reading instead, give them an angry look and tell them they're just wasting time. (Or laugh at their joke, haha &mdash; and then tell them that they're wasting time.)

Note that some of the Un-cards are too crazy to really stand up to this kind of rigor. You will have to just do your best to make sense of a weird situation at times, but honestly this isn't nearly as big of a muddle as trying to play Magic with old-school rules.

Easygoing casual play: use "common sense" and don't sweat it

The Un-sets aren't really designed for attention to detail and exacting technical play anyway. Arguably part of the "joy" of them is experiencing Magic with a newbie's sense of wonder and discovery (though this is rather personal and your mileage may totally vary).

So, just play like you're still figuring out the game. Try to do what the cards say as best as you can. Don't stress about what the "real" rules are. Don't get technical or demand precision from players at the table. If the game state gets too complicated due to some interaction of the cards, have the group make up something that sounds halfway fair and just move on.

If it helps, imagine you're twelve. (No offense to twelve-year-old "Spikes" who play tournaments and love the comp rules. In fact, mad props to twelve-year-old "Spikes" who play tournaments and love the comp rules!)

I recommend this approach if there's a significant skill gap within the group, or if you intend to play Magic while intoxicated.

Zany nonsense: make stuff up


  "If Floral Spuzzem attacks an opponent and is not blocked, then Floral Spuzzem may choose to destroy a target artifact under that opponent's control and deal no damage."
  
  "But... how does it decide?"


Some people look at Unglued/Unhinged as an opportunity to joke about playing Magic rather than play Magic per se.

If that's what your group is doing with their silver-bordered cards, then all sense of consistency goes out the window (with the exception of appeal to precedent, maybe).

At this point nothing an outside authority says about the rules is meaningful at all. So just make up your own interpretation and accept that you're playing Mornington Crescent.