I know it's per employment. There's no rule saying the max OW contribution per month is $2220. It could be $4440, but I'm arguing that due to the Annual Limit, it will stop after 6 months.
That's your argument, but there's nothing in the CPF Board's employer guides that say "stop CPF deductions after X months once the CPF Annual Limit is reached" or anything like that. Where do you see that? Why would the CPF Board fail to publish that important payroll processing detail in its employer guides if it existed?
The AW calculation is
also per employer, by the way. The CPF Board offers a
special provision for employee transfers between affiliated companies in Singapore. Why would this special provision even exist if your hypothesis is correct?
How do employers coordinate their payroll deductions for CPF? Where are the CPF Board's instructions on how employers coordinate payroll deductions if your hypothesis is correct, that they stop contributions after X months? Where are the facilities so that each employer can check other contributions? For example, is there some (unknown to everyone, apparently) API that employers' payroll systems can access to coordinate deductions?
You've got a hypothesis, sure, but where's the evidence for it? Literally everywhere it can say it, the CPF Board says that compulsory contributions are calculated per employer, not per member. As linked to already, it then says that there are two special provisions: (1) an employee can optionally choose to opt out of his/her compulsory contribution share above the CPF Annual Limit (but, pointedly and clearly, not the employer's share), and (2) an employer, with the employee's informed consent, can transfer an employee within Singapore between affiliated entities while treating the two affiliated entities as a single entity for compulsory contribution calculation purposes.
Let's review
the published CPF Annual Limit definition carefully:
CPF Board said:
CPF Annual Limit
The CPF Annual Limit is the maximum amount of CPF contributions that can be credited to an individual's account in a year. It consists of both the mandatory contributions (employer's and employee's share) and voluntary contributions.
First of all, this definition isn't quite true (or at least it's stretched pretty far, probably to the breaking point) even if you have one employer. The CPF Board considers contributions via the Additional MediSave Contribution Scheme (AMCS) to be Voluntary Contributions (capital V, capital C), and AMCS contributions can exceed the CPF Annual Limit of $37,740 (a figure the CPF Board routinely cites). So we already know this definition is suspect as literally written since it probably contradicts what the CPF Board has published elsewhere. The CPF Board isn't perfect. None of us are. Writing with clarity is hard!
When confronted with conflicting and suspect information, it's only rational and logical to assume that the more detailed information about specific terms and conditions -- specific guidance provided to employers on how to process CPF deductions, as a notable example -- is the more reliable information. If hundreds or thousands of employers were/are deducting CPF contributions incorrectly, it's reasonable and logical to assume that the CPF Board would be working hard to try to fix that. There's no such evidence.
However, in this case the formal definition can be interpreted consistently with the concurrent employer provisions. It says "employer's and employee's share" -- singular employer. It doesn't say "employers' and employee's shares," and it certainly could have said that. What happens when there are multiple employers? The CPF Board provides detailed written guidance, and we should be able to rely on it.
Better stop arguing with him. That time, he also insisted on the limit and only brought up AMC to prove his point ... nothing else. Knowing now, he provides link ..... 
