Most likely the upgrades cleared for people who asked before you did (it happens).

Maybe some did buy full-fare J tickets.

Relax, and your upgrade will probably come thru.

And if it doesn't, get to the airport EARLY to get back on the list.

When you say "plenty of seats available in C" I assume you really meant "the seat map shows open seats in J." And you realize that seat maps and fare class availability have nothing to do with each other, right?

The seat maps always seem to show unselected seats even though there is no availability.