Hi,

Some of your annuals may reseed and return. Once your biennial bloom in their 2d year, they should set seed before dying and return the following year. Perennials often need 3-5 years to mature, but you should see reseeding in those as well.

Much of this is dependent on the site. If you have a thick mulch layer, the seeds won't be able to reach the ground and you won't see very much reseeding. If you weed out small seedlings thinking they may be weeds, you won't see them mature. 

It is worth knowing that some of the seeds are invasive and or problematic here in Michigan and other states with climates similar to ours. One example is baby's breath: https://www.habitatmatters.org/babys-breath1.html

You're encouraged to research each species prior to purchasing 'wildflower' mixes. 

Michigan Native Plant Guild is a statewide group of native plant growers that you may find helpful. Some of them offer seeds and seed mixes for various site conditions. https://www.nativeplantguild.com/

Happy gardening!