Having 2 ARC the same time - possible?

have a student-ARC on a Taipei City Address (expiring October 07)
as i am married I think about a visa run and applying for a JFRV and new ARC with Tanshui address,
while applying I may lie to them and telling I had lost my student-ARC …
Issueing ARC’s in different countiers, do they cross-check ??

Simple answer: no.

Long answer: If you lose your ARC they will tell you to pop down the the immigration agency to get a replacement (and pay a few hundred bucks to do so). If you want to apply for a new resident visa they will need you to cancel the old one first. If you want to enter Taiwan you can only have one visa/arc active. And no, it is not possible to have more than one ARC at a time.