The Enhanced Retirement Sum limit is calculated to include prior withdrawals. What you take out of a CPF Retirement Account effectively reduces your ERS, dollar for dollar.
In 2021 here are the Basic, Full, and Enhanced Retirement Sums:
BRS = $93,000
FRS = $186,000
ERS = $279,000
So let's suppose you celebrate your 55th birthday this month (November, 2021), and your CPF Retirement Account is funded to the Full Retirement Sum (from SA and OA). You then immediately withdraw $93,000 (the BRS) with a property pledge/charge in place.
OK, now you change your mind in December, 2021, and you want to deposit $186,000 into your CPF Retirement Account to push the balance up to $279,000 (the ERS). Can you do that? No, sorry, not allowed. The ERS is calculated inclusive of withdrawals. The most you can add back in 2021 in this example is $93,000, not $186,000. In other words, a withdrawal from your RA permanently and irrevocably reduces your effective ERS limit. (Unless CPF changes the rules, but this rule has been around a while and seems unlikely to change.)