Trying to identify Manufacturer of some chip and best practice question

[Neurotox]

Hello,

I have 3 different model of 4N35 and they seems to have different specification.  It's standard for the same model number to have different (electric) specification depending of the manufacturer ?

If so, is their any easy way to identify the right manufacturer ? 

Data on chip:
-4N35 031ATK63 (ATK it's probably something...)
-K4N35 0744 (The K seems to make it easy,it's probably a Kondenshi)
-4N35 V 528 25 (Maybe a Vishay because it's came with a Arduino(Genuino) starter kit and on their web site they give the Vishay datasheet...and because of the V ?)

From Vishay and Kodenshi the spec are a little bit different so I presume it's standard to have different spec depending of the manufacturer.

Should I try to always stick to the same brand ?  Where I bought my stuff they don't seems to care, in my last purchase I got some 4N35 031ATK63 and some K4N35 0744...

I noticed the difference in spec by taking a resistor(Ohm) reading at the output of the octocoupler.

Thanks!


(english is obviously not my first language, sorry for mistake)