They assume his youthful skin and seemingly age defying appearance to be the byproduct of all next big thing in skincare, a creak or treatment that would become the all the rage among the rich and vain - a result of sharp knives and needles filling his insides with a serum too expensive for anybody who couldnt afford to live in their own ivory towers to afford. They never make the connection to the other serum.
The thing with SHIELD is that they ask him for a lot. A blank cheque here and there to cover the costs of programs and operations that even after multiple hints and suggestions they assume he has no knowledge of. They ask him for his tech and his genius in all sorts of avenues, but if there ever was any organization that understood just how pivotal Howard was to that elixir of miracles it was SHIELD. And yet they never asked.
Perhaps it was a consequence of his own making. His carefree attitude and lazy false persona made it easy for people to forget that he was the man behind all the inventions STARK industries marketed so loudly these days. A challenge like that would have normally spurred to many sleepless nights spent in his lab. Going through the numbers, weighing the consequences of success and of failure in his head. Perhaps they all just forgot it was a possibility or they were afraid of the side effects of success too.
The question they never asked him was how to reformulate the serum.
Many had tried with what little notes the team that developed it has left behind, but Howard, it seemed had just shown up one day with a vial and the scent of something dark and better forgotten about him and so his team never asked either. They closed their eyes to the dark eyed baby too young to know to understand the horror able things men are capable and never questioned how Howard and Maria got him to be so damn quiet when their own babes used their tears and cries - the only method of communication open to them. As if, the even as a baby, Tony knew something they did not. They closed their ears to that faint screaming sound that would echo in the corridors as the boy became older and skittish in the company of anyone other than that butler.
They closed their hearts to the fact that they never really saw him again after Howard's breakthrough. The only glimpses of him they got were what the rest of the world received too. A photo in a magazine here and there, celebrating his achievements or relishing in some scandal.
After all, no one would have thought the secret to Tony's effervescent appearance was an X. No one ever figured out that in essence the gift that was given to the good Captain was the watered down curse of immortality Tony was haunted by.