Hello Shane,
the only difference is the packing. Please refer to the product info page: https://www.nxp.com/part/LPC1769FBD100#/
LPC1769FBD100, 551 = Packing: TRAY-Tray, Bakeable, Single in Drypack
LPC1769FBD100K = Packing: TRAY-Tray, Bakeable, Multiple in Drypack
LPC1769FBD100/P1K = Packing: TRAY-Tray, Bakeable, Multiple in Drypack, manufactured in another fabrication site
Have a nice day
Pavla
The link you response does not call out the "manufactured in a different fabrication site.