According to one of the thought leaders in strategic account management, Olivier Riviere, the key thing you keep in mind to have a firm grasp on account management is “True key accounts have a special strategic meaning for the company, beyond their size. Make a clear distinction between large accounts and key accounts.”
Observing the account management process for quite a while may not easily translate the process well enough in many cases.
It is a long and cyclic process that takes time, effort, and money. However, those value accounts are likely to depart from the business relation anytime. In other words, it may be snatched by other businesses similar to you.

The client who has been with you for years would be a coveted lead for your competitors. Hence, the chance to lose them is high and it completely relies on how good your customer account management strategy is.