I've been watching the Terminator films recently, not seen them for a while, besides the fact that my Terminator DVD had a layer of some gunk on it that had to be cleaned off, I'm not the only person I know in the UK that's had this happen to their disc, so if you have the Region 2 of Terminator and ain't looked at it for a while then check your disc.
Anyway what struck me in Terminator was his hair, the Series 800 Model 101 Infiltrator unit's come off a production line so you'd assume they'd all have the same hair, it's not until 36 minutes into the film after he's been through a fireball in the back alley that Arnie gets the now recognizable spiked hair we associate with the Terminator, yet at the beginning of T2 he shows up with pretty much the same spiked haircut, and not the one we see him with at the start of the first movie.
The background to the screenplay states that after Kyle Reese is sent through to follow the first Terminator they realize that another unit, the T-1000 has been sent through so they program another Series 800 and send that through to help John Connor out. The script for the sequence where they send Kyle Reese through time and then walk into the warehouse full of unactivated Terminators can be read in script form with concept sketches in Terminator 2: Judgment Day - The Book of the Film - An Illustrated Screenplay. Cameron wrote the whole opening with the Time Displacement Machine but it was deemed to expensive to film. Once the second Terminator gets sent through the rebels are all set to rig the whole complex and blow it up.
Also it's not until the Series 800 damages his eye in a fight that he's forced to wear sunglasses to hide the damage in the first Terminator movie, yet in T2 he seems to wear the shades from the off, more like a fashion statement.
As for Terminator 3: Rise of the Machines I watched a version called Terminator 3: The Coming Storm off Fanedit.org in which lots of cheesy and unnecessary elements were removed as well as all the references to dates and ages that contradict the previous two films, with a new running time of 1h 28m as opposed to the original 1h 49m.
Again in Terminator 3: Rise of the Machines he sports the spiked hair and sunglasses.
The word is during James Cameron's divorce with Linda Hamilton, she asked for the Terminator franchise rights which she promptly sold to Carolco Pictures owners Mario Kassar and Andrew G. Vajna.