Hmmm.....
I am not sure if I get it.
The statement has been made that you cannot have upgradeable city facilities which culminate into a cultural centre because we must start with cultural centres.
If the above is true, then using another example, if the HW starts with Ship Yard 3, then we would not be able to upgrade to Ship Yard 3 from Ship Yard 1 or Ship Yard 2.
Even if the above is true, we could had a upgradeable city facility to a Kultural Centre (spelling intended) where the Kultural Centre is identical to a Culural Centre.