I am about to request an ED visa valid for a year, my understanding was the visa has to be utilized latest 3 months following issuance date and I would be able to stay one year as of entry date, but my consulate told me it is visa issuance date that is taken into account?? Since the officer I talked to was not aware of what is an ED visa, I am doubting, I would appreciate if somebody could clarify!

Any multi entry non immigrant visa (which a one year ED would be) is valid for 90 day stay only. You can exit and return for a new stay of up to 90 days any time during the one year validity.

To stay for one year without leaving you must obtain a one year extension of stay from Immigration inside Thailand and that would only require a single entry ED visa if you were qualified for it.