I have a Sears sport girls bike. S/N 502 451 33 827499. I want to know what year it is

I am sorry to say that the year is not very important. Sears bikes, except perhaps for JC Higgens ones, are not very collectible/valuable at all, and girls bikes always less so. As other companies made bikes for Sears there is no consistency at all in serial numbers that would allow you to date the bike. The first three sets of numbers refer to Sears (502) the model (451) and number of speeds/style (33). I don't know how to decode model - do a google search.

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