I have never heard of an Intel plant in Costa Rica. To my knowledge, Celerons are fab'd / made in Malaysia or Ireland. My C366 is from Malaysia and was manufactured week 21 (e.g., L921XXX...). It overclocks really well and is currently stable at 525MHz!
Of course some are made in Costa Rica. While is is true the Malaysian are generally better for overclocking not all will overclock even when one from a known 'good' week is bought. I suggest you look in an o/c database.
I have a week 28 Malaysian 366 PPGA that won't boot into Windows at all even at 2.20v at FSB100. I'm aiming for 550 and nothing else because I don't want problems with hard disk or video card.
I have a week 31 Malaysian 300a PPGA that in the same ASUS slotket with the same heatsink/fan combo runs on my BE6 at FSB100 at 450 at 2.0v. It went straight into Windows 98SE and I've been on the net for 90 min already without any problems. CPU temp is 34 C and Rain 2.0 does nothing at all!