I don't think this has ever been mentioned here before. Of course, if it were not 3.30 AM and I were not awake, it would not be mentioned at all. But be that as it may, here goes.
Bosco, of course, is the classic chocolate item... George's ATM code... the dying word of J. Peterman's mother (right? aunt?)... We've heard it several times this season.
But go BACK. Back, I say, to several seasons ago. The episode is "The Cable Boy." Synopsis: the K-Man gets the Sakharov of Cable Guys to install illegal cable in Jerry's apartment whilst Elaine hosts a shower for an old college friend who's marrying a Kennedy affiliate. George finagles an appearance at the shower to confront the mother with his stained red shirt, which had been ruined in a date with said mother at a performance art show in which she made dinner for God on stage.
Once, and only once, in that episode, George referred to what soiled his garment as "Bosco!" Elsewhere, he just termed it a container of chocolate.
I find this a compelling early indicator of the prominent place Bosco later occupies in this series. I don't know which season "Cable Boy" was, but judging from Elaine's wall of hair, I'd say at least a couple of years prior to the ATM fiasco.
Emily