Seeds in open packets can be very suseptible to damp or changes in temperature, as well as ageing. You don't say where your seeds are germinating - in an unheated greenhouse or a warmer windowsill indoors which could make a difference. Also, seeds of difference sizes take different lengths of time to germinate. Most packets should last two years if stored in a cool dry place. Possibly yourmarigolds and verbena don't like the lower night temperatures. Wait a few days and if nothing much has happened perhaps you need to try some fresh seed.