The subjunctive in Spanish is mainly used in subordinate clauses, and its use largely depends on the main verb and on its form (affirmative or negative) and tense.
With verbs of mental process in the negative, the negation (1) can refer only to the verb of mental process (in which case the indicative will be used) or (2) can refer to the whole sentence, "que"-clause included (in which case the subjunctive will be used).
Negation is said to be used contextually in (1) and to express a personal doubt in (2). For example, if we say:
No cree que me odian. (They hate me, but he does not believe it.) Here the negation only refers to the verb "creer".
No cree que me odien. (He doubts that they hate me.) Here the negation refers to the whole sentence, "creer que me odian".
There is a problem with the verb "pensar": in the negative it does not work well to express a personal doubt IN THE FUTURE (it can effectively express a personal doubt SIMULTANEOUS WITH THE TIME OF THE DOUBT or IN THE NEAR FUTURE). The problem is that, unlike "ser efectivo" below, the verb phrase "salir a la luz" necessarily points to the future.
1.a. No pensamos que el plan sea efectivo (We don't think that the plan IS effective).
2.a. No pensamos que el plan será efectivo (We don't think that the plan WILL BE effective).
or in the past:
1.a'. No pensamos/pensábamos que el plan fuera efectivo (We didn't think that the plan WAS effective).
2.a'. No pensamos/pensábamos que el plan sería efectivo (We didn't think that the plan WOULD BE effective).
At the same time, its synonym "creer" does not work well to express contextual negation. To fully understand the difference between (1) and (2) with "salir a la luz", let's see how "no pensar" is used to express contextual negation and how "no creer" is used to express a personal doubt:
Where "pensamos" is used, we should note that it can mean "we think" or "we thought":
1.b. No pensamos que el plan saldrá a la luz pronto.
2.b. No creemos que el plan salga a la luz pronto.
Although both sentences can be translated as:
"We don't think the plan will come to light soon",
1.b. really means: People say the plan will come to light soon (they are certain about it), but we don't agree, while 2.b. means: We are doubtful about the plan coming to light soon.
Similarly, in the past we have:
1.c. No pensamos que el plan saldría a la luz pronto.
2.c. No creímos que el plan saliera a la luz pronto.
Both sentences can be translated as:
"We didn't think the plan would come to light soon",
but while 1.c. means: People said the plan would come to light soon (they were certain about it), or the plan did come to light soon, in spite of our disbelief, 2.c. means: We were doubtful about the plan coming to light soon.
In the imperfect, the subjunctive shows the same feature as with the preterite:
1.d. No pensábamos que el plan saldría a la luz pronto.
2.d. No creíamos que el plan saliera a la luz pronto.
With a verb like "dudar" in the affirmative, the subjunctive will always be used, because the personal doubt is obviously implicit in the main verb itself (there is no contextual negation here). As is the case with "pensamos", "dudamos" can be "we doubt" or "we doubted":
Dudamos que el plan salga a la luz pronto.
Dudamos que el plan saliera a la luz pronto.
Dudábamos que el plan saliera a la luz pronto.
(3) means "We doubt the plan will come to light soon", while (4) and (5) mean "We doubted that the plan would come to light soon".
Reference: http://www.hispanoteca.eu/Foro/ARCHIVO-Foro/No%20creas%20que-subjuntivo%20o%20indicativo.htm
http://www.hispanoteca.eu/Foro/ARCHIVO-Foro/No%20creo%20que-subjuntivo%20o%20indicativo.htm