How does a person know which he is up against? And theoretically speaking, how should one tackle each?

What I do is slow my ball speed way down and see what happens.  If it is heavy volume; typically the pattern is no longer than 42 feet as centers wont want carry down all the way to the pin deck (can create nightmares for the lane mechanics).  Long oil is typically a light to normal oil volume.  If I throw it slow and still get some backend motion; then I believe it to be heavy volume normal to longer length pattern.  If I throw it slow and the ball still doesnt do much on the backend; then I think long oil (longer than 45 feet) with lighter volume.  The transitions will be different as the long pattern will break down a little quicker in the fronts and midlane whereas on the heavier volume it will tend to carrydown before it breaks down.  Watching your ball reactions are a must in determining which one you are encountering.

Ahhh! Thank you

There's an old PBA saying of letting your ball be your guide. It still holds true.

I experienced something similar to Bill O'Neill last month at a gig. The tournament director does not post their pattern(s) prior to bowling, but they will post what it was after the tournament. Because of my ball reaction, I was under the impression I was bowling on an intermediate pattern of about 38 to 39 feet. I was quick to recognize in practice anything 9-board and out was out of bounds.

Making this response short, it turned out the pattern length was 44 feet and it was the Kegel Dead Man's Curve; a pattern that is right at or just under 3:1.

For me, it played anywhere from 11-board all the way into 18-board depending on ball choice and where I lined up on the approach. I also used a Platinum Ringer, Slingshot, and even my old Columbia Black U-Dot. I finished 7th out of 123.

The guy who won, if memory serves me correct, used an IQ Tour Pearl, Venom Shock, a Tribal; the ball he used to win the tournament was an Octane. We both played similar break points.