Encounter at Farpoint (1) - S1-E1
Character mistake: In his exchange with Admiral McCoy, Data uses several contractions (i.e., shouldn't, I'm). For the rest of the series he doesn't, and in S3: Ep16, "The Offspring", he admits that his programming makes him incapable of using contractions. And in S4: Ep8, "Future Imperfect" Riker questions Data on when he started using contractions, knowing that Data is incapable of it.
Where No One Has Gone Before - S1-E6
Character mistake: Mr. Kosinski is trying to explain what happened to allow them to travel so far. He says, "I applied the energy asymptomatically", when he meant "asymptotically." (The subtitles for this scene are correct). (00:13:50)
Character mistake: When the away team transports down to the planet, Data is wearing three full rank pips denoting the rank of a full Commander, rather than his actual rank of Lieutenant Commander. (00:09:39)
Character mistake: At the end of the episode, after Lore has been defeated, Picard asks Data if he is O.K. Data replies, "I'm fine." One of the plot points of this episode is that Data cannot use contractions.
Suggested correction: That characteristic was not added to the character until season two. In the first season, Data uses contractions on a number of occasions.
It's still a possible mistake, even if it wasn't part of season 1 scripting. Just because we only learn later that Data doesn't use contractions, doesn't make this mistake invalid. We learn Data was specifically constructed that way and hadn't been able to use contraction since being created, which means all of season 1 he shouldn't be using contractions. Although it would probably be best to submit it as a mistake in season 2 when it's mentioned that it contradicts what was established.
It would only be a mistake if he used the contraction after the trait was established for the character.
Possibly, but that's not how mistakes on this site work seem to work. It could still be a valid mistake in the context of the entire show since the character trait had in fact been established. It's the same way for when shows do something like establish a character's birth-date in later seasons, but when episodes from earlier season have the character at the wrong age. Although it would probably be best to submit it as a mistake in season 2 when it's mentioned that it contradicts what was established.
We'll Always Have Paris - S1-E24
Character mistake: When Data is on the planet, about to drop the material into the temporal rift, one of the three Datas asks which one of them should do it. The middle Data replies, "Me. It's me." Data is meant to be incapable of using a contraction.
Suggested correction: That character trait was not established until season 2. Data uses contractions multiple times in the first season.
While it was explicitly expressed in season 2 that Data can not use contractions, the fact that they did established this character trait means it could be a valid mistake since the trait is meant to show Data could never use contractions since his creation, not that he suddenly developed it some 30-odd years later. Although it would probably be best to submit it as a mistake in season 2 when it's mentioned that it contradicts what was established or at least make one character mistake for "all of season 1" than list every individual time it happened.
Suggested correction: It is true that in later seasons he is unable to use contractions. However, since that characteristic was not introduced in the first season, this is not a mistake. His behavior is consistent with the character's behavior throughout the first season.
It's still a possible mistake, even if it wasn't part of season 1 scripting. Just because we only learn later that Data doesn't use contractions, doesn't make this mistake invalid. We learn Data was specifically constructed that way and hadn't been able to use contraction since being created, which means all of season 1 he shouldn't be using contractions. Although it would probably be best to submit it as a mistake in season 2 when it's mentioned that it contradicts what was established.
Bishop73
Incorrect. It would be a mistake if he used a contraction after the trait was added to his character, but the mistake can't be retroactive as it wasn't a mistake for him to use it at that point in the show.