b) Second level: LG 25: "Although the individual bishops do not have the prerogative of infallibility, they can yet teach Christ's doctrine infallibly. This is true even when they are scattered around the world, provided that, while maintaining the bond of unity among themselves, and with the successor of Peter, they concur in one teaching as the one which must be definitively held." This means: (1) The day to day teaching of the Church throughout the world, when it gives things as definitively part of the faith, (2) If this can be done when scattered, all the more can it be done when assembled in Council. Thus Trent (DS 1520) after "strictly prohibiting anyone from hereafter believing or preaching or teaching differently than what is established and explained in the present decree," went on to give infallible teaching even in the capitula, outside the canons.
To know whether the Church intends to teach infallibly on this second level, we notice both the language -- no set form required - and the intention, which may be seen at times from the nature of the case, at times from the repetition of the doctrine on this second level.