The comet we know as 2P/Encke
was "discovered" many times, including by Caroline Herschel.
However each time it was considered to be a different comet . . . until German astronomer Johann Encke worked out that several "discoveries" were reappearances of the same comet coming back every 3.3 years. French astronomer Pierre MÃ©chain was the first person to report it, but it was named for Encke when he correctly predicted its return.
The "2P" means that the comet is the second known periodic comet, one that is known to return. The first, of course, was Halley's Comet
whose return was correctly predicted by Edmond Halley.
Image credit: Damian Peach