If Snape had seen James transform into a stag to save him, I find it very difficult to believe that he wouldn’t have told anyone. He’d certainly have told Dumbledore at the very least. And if Dumbledore had known that James was an Animagus prior to the end of POA (I’m assuming that he had a conversation with Sirius while Harry was unconscious), people would have been a lot more careful come POA to keep Sirius out of Hogwarts, because it was known that James and Sirius were inseperable (though many would still not think to include Peter) and that Sirius was likely one as well. And since we know from POA itself that Snape will drop hints and try to find ways to tell people something about someone he dislikes even if he’s been told to keep that a secret, I find it unlikely that Snape would have never dropped any stag hints to Harry in those first three years if he’d known and Harry didn’t.
The simple fact of the matter is that a certain segment of Snape fans will shit relentlessly on James, jeering at the idea that he matured and changed from his bad teen behaviour and stopped being a bully, preferring to think that Lily was just too gullible and stupid to know James’ true self (or else selfish enough to not care because he’s rich). They sneer at the idea that James spent three years working his ass off to become an Animagus for Remus, because somehow that counts as a selfish act, not a brave compassionate one. They discount that he saved the life of someone he hated because oh, he wasn’t really putting himself at risk, and anyway he didn’t do it for the sake of the person he hated (who he also bullied, did we mention that?), he did it for the sake of someone he liked so it just doesn’t count. And any character who says anything that contradicts that view of James (no matter how well they knew James and the sort of things he’d be likely to do) must be ‘polishing up the story dishonestly on the fly’.
And okay, fine, they’re free to say so. But then they seem really confused and even genuinely hurt as to why people apply those exact arguments to Snape. They’re bewildered that anyone would even dream of pointing out that Snape’s adult behaviour involved bullying others and that there’s not much to admire there, because to some of them Snape wasn’t a bully at all. They can’t get why people aren’t swooning over Snape risking his life to save Harry for Lily’s sake (which suddenly becomes admirable and romantic as fuck) by… sitting on his bum and staring at Harry and his broomstick really really hard while mumbling under his breath, because gosh, such a risk he was taking! His clothes caught on fire, doncha know? Also, Hermione is bad for daring to set said fire in an attempt to save Harry’s life, because she should have somehow assumed that Snape was trying to save the life of a kid he hated and bullied (and continued to bully afterwards). But Snape is totally kosher in thinking that James was in on the attempt to get him killed, because he’d been bullying Snape and continued to do so afterwards.
The double standards, they burn.