It is obvious from Bruce’s account that the material eventually released on Polydor is the stuff the Shadows wanted to be doing - and making money from - and that EMI were not interested in merely leasing it.
After 22 years of devoted and loyal service to EMI they in effect slammed the door in our faces. They must've made a vast amount of money from sales of Apache over the years considering how many times it has been featured on compilation albums. It took 20 minutes to make and cost the company a negligible amount of money.
So the Shadows went on to own all their new material. They set up Roll Over Records to manage the business and leased the product to Polydor, leaving EMI to make the best of what they had in the can. As I see it, EMI cobbled together Another String against Change of Address in a successful, if blatant, attempt to milk the cash cow for possibly the last time.