When it comes to 1975, they based that off what they thought were 7000 year creative days. That idea went back to the 1820 with Henry Finnes Clinton and to William Miller. So we can't really blame Fred Franz for that. It was open ended and the numbers pointed towards the future. But they didn't understand. They all didn't understand that the creative days were not 7000 years long. The six days of creation listed were actually 6 24 hour days, but the events within encompassed millions of years.
As for 1925, I had totally forgotten what the calculations were that Rutherford used. That shows how insignficant it is.
But as far as the old books go; I can understand how they say get rid of them and don't use them because it is a totally different organization from the one that produced those books.