CRW:
Thomas sets up a case in point for the latter part of your preceding paragraph, and this is where you will find the exception for the one year allowance.
Italics Summa
But to actual confession a man is bound in two ways.
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First, accidentally, viz.
when he is bound to do something which he cannot do without committing a mortal sin, unless he go to confession first: for then he is bound to confess; for instance, if he has to receive the Eucharist, to which no one can approach, after committing a mortal sin, without confessing first, if a priest be at hand, and there be no urgent necessity.
Hence it is that the Church obliges all to confess once a year; because she commands all to receive Holy Communion once a year, viz. at Easter, wherefore all must go to confession before that time.
The next paragraph leaves the exceptional cases behind and deals primarily with instilling urgency of confession.
Secondly, a man is bound absolutely to go to confession; and here the same reason applies to delay of confession as to delay of Baptism, because both are necessary sacraments. Now a man is not bound to receive Baptism as soon as he makes up his mind to be baptized; and so he would not sin mortally, if he were not baptized at once: nor is there any fixed time beyond which, if he defer Baptism, he would incur a mortal sin. Nevertheless the delay of Baptism may amount to a mortal sin, or it may not, and this depends on the cause of the delay, since, as the
Philosopher says (Phys. viii, text. 15), the will does not defer doing what it wills to do, except for a reasonable cause. Wherefore if the cause of the delay of Baptism has a mortal sin connected with it, e.g. if a man put off being baptized through contempt, or some like motive, the delay will be a mortal sin, but otherwise not: and the same seems to apply to confession which is not more necessary than Baptism.
Moreover, since man is bound to fulfill in this life those things that are necessary for salvation, therefore, if he be in danger of death, he is bound, even absolutely, then and there to make his confession or to receive Baptism. For this reason too, James proclaimed at the same time the commandment about making confession and that about receiving Extreme Unction (
James 5:14,16). Therefore the opinion seems probable of those who say that a man is not bound to confess at once, though it is dangerous to delay.
The correct way to read 1457 then is that once a year a confession is cumpulsory, disposition irrelevant, not that an individual has a year to confess his mortal sin.
AndyF
