FDA current 5 criteria in '06 when those require the immune data that had not been presented until later?
Actually immunogenicity is not one of the five criteria for sameness. If I recall correctly, immunogenicity was kind of an "add-on" to the other criteria.
It is certainly possible that Amphastar was told they had met "sameness" early on, and they extrapolated this themselves to the claim that they had met the five criteria.