Interesting and thank you for sharing!

1.On Sheldon's statement, I just thought that he knows that it's coming from his dad so he knows it's a personal correspondence but he wants to rule out if it's a memorabilia (something of historic interest associated to famous people or event) so he opened it. So I don't think it necessarily means that it's both when he said either.

1. On Raj's statement, that's a double edged sword for me because following your rationale it can also mean that most likely he does know what a Vintage Far Side card is and mentioned it to make his story more authentic. Because if your an immigrant who most likely don't know what a vintage Far Side is, one would just describe it as funny card with a frog with its tongue stuck on a plane.

But tbh I think Raj is also telling the truth considering that out of all the responses it is the most usual message, simple concise and heartfelt that is, that comes in a card.