Yes and no. Let’s see how.

When the action is finished in the past one uses the passé composé form of the verb (together with the auxillary). Since “regarder” is transitive, the auxillary is “avoir” and hence the corresponding form for the first person plural.

When the action is described in sense of “was being undertaken/used to be” with it’s completion being left vague, then the imparfait is used “nous regardions” (without the auxillary avoir) and directly conjugating the main verb.

(In my experience) In normal conversations though the French speakers seem quite intelligent and can make out what you want to convey by the context, tone and sense.

You need to make a difference between the Conjugation Chart and the use of the verb forms. If you look for Preterit in a French Conjugation Chart, you will find the Passé Simple. But in fact, in French, we use the Passé Composé when English use Preterit. It’s a question of habit, of language evolution.

French and English do not make the same distinctions between past tenses. You cannot determine which tense to use in French from the tense used in English, you have to use the meaning.

“**Nous regardé*” is not grammatically correct. Regardé is a past participle, you can’t use it on its own in a sentence.

“We watched TV last night” denotes an action that took place at some time in the past. The correct tense for that is passé composé: “Nous avons regardé la télé hier soir”. In literary French, you will also find passé simple in similar circumstances, but it is not used in daily life, even in writing.