THSB: Two-Headed Singer Bands

I was driving home the other day and I realized most of my favorite bands have in their history two lead singers at the same. When one lead singer is no longer, the other can carry on. As a band member, I think having two lead singers is like an ace in the back pocket. As a fan, I think having another lead singer means your favorite band will continue to make new music. Your band can survive with two lead singers due to attrition.
For example Genesis had Peter Gabriel and Phil Collins took over. A band like ACDC had Bon Scott and then hired Brian Johnson after his demise which does not qualify as THSB because Brian had not been in the band prior.

The criteria for THSB is as follows:
1. At least two lead singers are in the band at the same time
2. Each lead vocalist must be the main vocal of at least one well-known hit (before or after each has either left or exited the band)
3. Lead singers can leave and come back as long as another lead vocalist remains in the band
4. When one lead vocalist leaves, the second vocalist becomes the new lead singer
5. THSB can operate with one lead vocalist but until another lead vocalist joins the band, however, it is reduced to OHSB (one-headed singer band) until rules 1-3 are invoked

Stay tuned for THSB bands! Do these rules make sense?