Actually a lot of Data's inconsistencies are the result of changes
in the writing staff -- not necessarily bad writing, just different writers coming and going and having different ideas about Data's character. As discussed above, the no-contractions thing was a retcon introduced midway through season 1, before which he'd been using contractions routinely. That was a bit of sloppy continuity due to the upheavals in the first-season writing staff. As for Data's lack of emotion, that wasn't overtly codified until "The Ensigns of Command" early in season 3. Originally, the idea was that Data was capable of emotion but that it was subdued and underdeveloped, a potential he hadn't fully realized yet. He was meant to be childlike and naive in his understanding of emotion, but not completely incapable of experiencing it. "Skin of Evil" and "The Measure of a Man" made it clear that he did have feelings for Tasha Yar. But for whatever reason, by the start of season 3 the producers at the time decided that they wanted Data to be totally devoid of emotion, a decision I've never understood.