Development of 1 year where you send to the customers the files edited or the full package to upload in their servers.
After an year you discover that they was doing patches of your code, fine but I need that. They sent to you that patches to be in sync.
After 1.4 years you discover that they have their own git unused and they want that we use that because they are bored to do manual patches.

Useless to say that we discovered that they was doing patches only when the system gone on production?