Is there a unified concept of the law of agency?

(First set out what agency is) Agency is a relationship between two parties where the Principal has authorised the Agent to act on his behalf and the Agent acts as such. The Agent is able to enter into contracts on behalf of the Principal and enter into legal relations on his behalf. An Agent can have actual authority or implied authority. This is where the Principal has expressly or implicitly given authority to the Agent. There is also apparent authority. This is different from actual/implied, as the Principal may not have given his authority to the agent. Rather he has, by words or conduct made a third party believe the Agent has authority. Although actual and implied authority can be explained through the consent argument, apparent authority cannot. Krebs attempts at creating a unified concept of agency through the idea that all types of agency are contractual. However, the issue with his argument is the case of Bolton Partners V. Lambart. An Agent here accepts an offer from a third party for which he had not authority. The third party attempted to revoke his offer when he learnt of the circumstance, but the Principal decides to ratify the contract after. The third party was bound by the contract. This is because apparent authority has retrospective effect, meaning the contract was made at the time the third party first accepted the contract. Consent can therefore not explain this theory as the law is based more on estoppel. There is no unified concept of the law of agency, as the different aspects were developed at different times for contrasting reasons.