During the authentication procedure, the certificate chain is verified by checking that all the certificates are valid and being used correctly. This includes certificate integrity checking, proper usage properties, and validity period. In case any certificate in the chain fails, the MIDlet suite will not be installed.
With respect to the validity period, it is important to consider that purchased certificates normally have a restricted period, often one or two years. Only during that time is possible to use the certificate to sign and install MIDlet suites. This implies that suites signed with a certificate cannot be installed after or before this period. It is important to keep this in mind to obtain new certificates when appropriate and sign again the MIDlet suites that need it.
However, any MIDlet suites already installed in a device will continue to function normally after the signing certificate is expired.