Promises at time of hiring

I live and work in Georgia. I have worked for a large city for 25 years. I had worked for this city for 6 years previously. We did not have a retirement plan for those first six years. Upon being interviewed for employment in 1978 I was told that if I would accept the job, I would be credited with the first six years as longevity for this term of employment which would increase my vacation time accrued and retirement time (Annual retirement pay equals 2% of salary per year worked). For all of these past 25 years I have been credited with the six years for vacation time which increases with each 5 years of longevity. For several years my employment date was shown as 1972 to account for the promised six years. At some time, this date was changed by our HR section to 1978, thus discounting the six years. I continued to get vacation time at the original rate. I have also continued to recieve recognition pins and letters (the last was a 30 year pin) Is it legal for them to change the original employment date which changes our original agreement thereby lowering my retirement pay by 12% of my annual income?

What did the plan manager (or HR manager) say when you asked them (in WRITING) for an explanation and that they correct their 'amendment'??

I was told that I would need the agreement in writing for them to accept it. The former HR director is now dead, so I cannot get a writen statement from him. I always assumed that since they lived up to half of the agreement it would not be necessary to have written proof.

You're not understanding my post. I was asking what did they say when YOU sent them a written statement detailing your earlier standing and asking them to explain their alteration of the previously existing record.

I have not previously requested an explaination from HR. I only spoke with a rep on the phone. I will do so now and return to you when I receive an answer from them. Thank you.