Validity Of Offer Letter

Dear All,
My company issues an offer letter after selecting a candidate which includes the designation, dept., clause of probation and notice period. Also the list of documents needed to submit on joining, if the candidate accepts the offer.
On joining, an appointment letter is issued which is a 4 pager. it includes, in details all the terms and conditions of employments, leaves, detailed break up of CTC, conditions of termination, employment anywhere else etc.
My question is that after the joining (i.e. signing the appointment letter) of the candidate, how valid is the offer letter? does it hold any value?

Detailed appointment letter supercedes the Offer letter. For all practical purposes, appointment letter only will hold good after joining of the employee. Offer letter is like provisional degree certificate issued by the college while passing out. Once you receive the degree certificate issued by the College/University, prov. certificate has become redundant.
Pon