It seems you have it correct, $42 per month is is $504, since that is under the stated limit of $1,000 you should receive an annual match of $252.
It does not say if the match is calculated and deposited each payroll or at the end of the year in a single deposit.
On the other hand if you were contributing $420 per month that would be $5,040 for the year. Since that exceeds the maximum $1,000 that is matched the annual match would be capped at $500.
In addition it appears that an annual contribution is made that varies based on pay and years of service with the company.
This is only a brief summary and the legal plan document and summary plan description might contain additional information that could effect eligibility and amounts.