Yevgeny Kafelnikov is at 9 in both singles and doubles. I have very little doubt that if he plays this year, it will be 10. What is the Open Era record? I know Sampras is at 11 in singles.. Anyone has more than him? And in both singles and doubles?
Well it may only be on one surface, but in 1995 Thomas Muster managed to rack up an incredible 12 titles on clay with a 7-title winning streak that included Roland Garros, as well as Monte-Carlo, Rome, Hamburg, Estoril, Barcelona...
I seem to remember his win-loss record on clay from 95 to 96 was something like 95-3, and those 3 losses were all to Spaniards who are rather well known today: Alex Corretja, Albert Costa and Carlos Moya.
Having reread your post, I've just realised that I've completely misinterpreted what you said and given the wrong answer, sorry.
To answer your question, I believe Ivan Lendl won at least one title every year for fourteen straight years, from 1980 to 1993, including his annus mirabilis in 1982 when he won fifteen titles. Mind you, he probably was the Eighties equivalent of Muster; John McEnroe said in his autobiography that Lendl's game was a prototype for the kind played by most clay-courters nowadays.