Do you have other samples to look at? I would think after 1 month it would be fine, unless it had been unfrozen or refrozen. Otherwise, it's too cold for bacteria etc.
I personally don't know if it's a different taste after freezing, but the separation of milk the bluish colours were what I found. My DD would accept both the breast and a bottle of frozen milk and not mind.
Trial and error might be your best bet!