In the Subscribers dashboard, New Accounts refers to brand new accounts that were created during that time period. Keep in mind that not all accounts have subscriptions attached to them. Some accounts may be open/active, but have NO subscriptions attached to them. They might not be ready to subscribe or they might be getting charged using one-time invoices only.
New Subscribers refers to a new customer who created their very first subscription. Note that one could have been an account-holder for a month or two before they actually subscribed to a plan, thus becoming a New Subscriber down the road from the time they were a New Account.
This is why those two numbers will not necessarily match in the dashboard - they are two different categories. One is counting accounts and the second is counting subscribers.