My aunt has a score of 835. Her mortgage was paid off 15 years ago. She has only had one credit card ever and it is over 10 years old. She accidentally missed one payment on the card and that was 6 years ago. She has several paid auto loans. She has had 3-4 old personal loans. Currently she has only her CC and an auto loan which is all she has had for the last 4 years. She's always paid more than the minimum on everything including her auto loans, most of the time doubling her payments. She rarely applies for new credit - only when truly needed but she knows she can get pretty much anything she wants, anytime she wants and at the best rates. (MUST BE NICE!)
She's never known about "scores" (until I brought it to her attention) much less pursued the perfect score. She really could care less about them now. The only reason she knows her score is because she considered trading in her vehicle and they told her her credit was perfect. I pressured her to call back and get her score from them. She's old school and simply concentrates on keeping her reputation perfect with creditors by paying on time all the time with everything. I think that alone goes a long way, especially long-term.
I think an absolute current mix of this and that and you must have X number of CC's is bologna. For the short term fix, maybe, but I think time is what matters most of all when it comes to the perfect score - based on her experience.