I had a quick Google for DS18B20 data sheets.One lists the temperature range as -67° F to +257°F (DalSemi)Another lists the range as: -67°F to +212°F (Maxim)There are probably more manufacturers.
I seem to recall that -196°F (-127°C) is the 'out of range' code and it is quite possible that the older ones you have don't issue an 'out of range' code and maybe just fail to give anything
Obviously, I don't know what you are using them for, if the +200°F is just used to test them or if you require them to read that high. If your using them with a micro-controller which I would assume you are as you are on this forum, then you could just add to your code to ignore the -196.6°F or print 'Out of Range' etc.For general purpose use though, I don't think you have a problem. If they work as a temperature sensor then great.
Have any idea about where to buy some that do work?
I've always found this seller Alice to be reliable. I've been purchasing from them for a number of years and have always received good parts. I personally like the fact that they have been around for a long time.
Most Ebay sellers all get there electronics sent from the same warehouse, so doesn't matter who you order from you just take you chance.
I've found as their reputation grew their price became a little higher, but these folks cannot be making much profit so I stick with them.
Please see the update to my previous post..
I placed an order for 10 last night. Please advise.