To be strictly in accordance with the grammatical rules, you should indeed also apply the concordance des temps with the subjunctive, therefore using either the subjonctif imparfait or the subjonctif plus-que-parfait for the simultaneity or the anteriority of the subordinate action, respectively.

This would thus be :

il fallait qu’elles trouvassent …

il fallait que tu vinsses …

In practice, as far as I can tell, most people use the subjonctif présent or the subjonctif passé instead, especially if you are speaking. So that you should not use the past forms when you speak if you don’t want to sound old fashioned. I find it a little sad, but that’s the way it is.

As a last remark,

il fallait qu’elles aient trouvé…

would be interpreted as an action that took place before "il fallait" because the subjonctif passé replaces the subjonctif plus-que-parfait in this (wrong but admitted in practice) context.