I dare say that I am revealing shameful ignorance, but I have the following difficulty. Suppose that the English sentence starts. “I was afraid that,” and the continuation is"
" the bull HAD escaped." Continuation in Latin is pluperfect subjunctive.
Both 2 and 3 would normally be timebam ne taurus effugeret. That’s formally ambiguous but in practice the context would likely resolve the matter. Similarly in primary sequence (timeo ne effugiat). Only in exceptional circumstances would the future participle be used.
The relevant A&G reference, though it does not deal expressly with the Latin ambiguity (and of course the English is antiquated), is 564. Gildersleeve 550 is clearer.