There is no statute of limitations for excess contributions, although the IRS has so far been reluctant to levy multiple year taxes and interest when they discover an old uncorrected excess contribution.
That's interesting. Do you have a source for that (the reluctance to impose multiple-year taxes/interest)? Unfortunately I have found them very willing to impose multiple-year taxes and interest, going back more than a decade. If they are imposing these penalties on some, but not on others, then depending on the reasons it could leave them open to legal action. But in any case, from hard, hard experience, do not count on them being reluctant to impose any taxes or penalties they think they can, even when they're wrong.
On the other hand, you can
withdraw excess contributions without penalty or tax if you do so before the due date of the return for the year of the contribution. You just have to be sure to withdraw (in addition) any interest or earnings that may have accumulated on the contribution. If there is a loss you can then take the loss as well. Usually all of this is handled by filling out a form and sending it to your broker. They then do the calculations to allocate interest/earnings to the withdrawn contribution amount. See IRS Pub. 590
. As far as I can see (I'm not a professional) there is no disadvantage to making an IRA contribution in the first week of January as long as you check your eligibility toward the end of the year and adjust accordingly.
The reason for the flexibility is obvious... nobody actually knows for certain what their annual earned income will be. Some will lose their jobs and make less than they expect. Some will do well and make so much that they end up over the limits. Some don't have a salary but depend on selling their wares as they go.
Note that in addition to withdrawing contributions you can also recharacterize them. There is a lot of flexibility as long as you don't go past the tax filing deadline. After that, you're cooked, and must deal with the issue as quickly as you can. The penalties add up very quickly.