Yeah, some manufacturers do use inverted pins 2/3. Martin did for a long time but they said it was a propriatory control system. At least they run all their fixtures the "correct" way now.
Another thing to be aware of is that the "true" DMX512 should actually use 5pins and you come across that every now and then so some 5 to 3 converters are handy.
I also always carry a couple of terminators as well, just in case I need them.