At present, the Shanghai Stock Exchange has at most 3 shareholder accounts and the Shenzhen Stock Exchange has at most 20 shareholder accounts. In other words, if you want to open a securities account that can buy shares of both Shanghai Stock Exchange and Shenzhen Stock Exchange, you can only open three. After opening these three securities accounts, the newly opened accounts can only buy shares of Shenzhen Stock Exchange, not Shanghai Stock Exchange.
After opening three accounts, you can also transfer money or close accounts, and then open a quota to reopen. If you have a dormant account, you usually need to cancel or activate the dormant account before you can open a new account.
Moreover, the latest regulations require all brokers to support online account cancellation, and the specific conditions for account cancellation can be asked by the brokerage customer service staff.
If you want to apply for both Shanghai A and Shenzhen A accounts at the same time, you don't need to specify when applying, just check the type of account you want to apply for.