I'm sure they made a reference to the additional family information when they mentioned the IMM8 form.I'm also sure they inform you to update your family information in reference to this.If this is the scenario,it's the Additional family information form IMM 5406 that is been requested.
Unless you have an addition to your family through marriage or birth of a new baby,Accra will not ask youth update Generic form.
If you have recently gotten married,added your new spouse or your new baby and have not sent generic form to Accra before now,i will strongly advice you to send both forms with reference to your new family composition.
In doing that,Accra will pick what is needed and shread the other form away.
Just include a cover letter to explain your motive of inclusion of the two forms.
Even though it's not my personal experience ,i know a couple of buddies that experienced it.
Cheers.