Well-Wishes came right after Letterbox – Indepentional and followed much the same style of ‘Only Dialogue’. Whereas Letterbox’s oddity was the Narnia-like post office in the boy’s closet, in Well-wishes it’s a mysterious, possibly magical, card for well-wishes. The gag with their ‘no-relation’ names didn’t carry over to this one mostly because the boys never interact with anyone beyond the two of them.
I’m racking brain to remember the inspiration. Beyond the obvious Letterbox, the main clue is me using the Ouroboros for the grandparents signature but ultimately I can’t say. I think Letterbox is the much better of the two so not knowing is hardly a great loss.