lawfag here
issuance of the indictment stops the statute of limitations
sealing is a separate issue
if the SL runs while the indictment is sealed too bad for the defendant
issuance is the key for that
only exception is if a defendant can show the indictment was sealed in bad faith or no reason but in these cases that should not apply
defense lawyers hate this - in effect a free extension of SL for the prosecution but again they have to justify it