Quoted from Fall 2009 Employee Plan News https://www.irs.gov/pub/irs-tege/fall09.pdf
Compensation limits vs. elective deferrals/§415 limits
Confusion may arise on how to reconcile the limits under §401(a)(17), §415(c) and §402(g) when an employee’s annual compensation exceeds the current §401(a)(17) limit. For example, can a 40-year-old employee earning $30,000 per month (annual compensation of $360,000) who elects to defer a flat dollar amount of $1,375 per month ($16,500 for the year) in 2009 to his or her 401(k) plan continue to make elective deferrals after September, at which time his or her yearto-date compensation exceeds $245,000? The answer is yes, because the plan is not required to determine a participant’s §401(a)(17) compensation based on the earliest payments of compensation during a year. Unless the plan’s terms provide otherwise, the $16,500 §402(g) elective deferral limit is applied uniformly to the $245,000 §401(a)(17) compensation that the employee receives throughout the year, regardless of whether deferrals are expressed as a dollar amount or a percentage of compensation in the employee’s salary reduction agreement.