Here's what I'm basing that on...
That's a reminiscence from Pat Peppler, who was Lombardi's vice president in charge of player personnel.
So that's not clear on exactly how much of a raise Kramer got, but it sounds like it was from $16,000 to something at least close to $23. This was in the era where most players had offseason jobs in lumberyards, construction. selling cars or insurance, etc. Turning down $23,000 woukld be a very difficult decision for Kramer.
I also recall reading once that Kramer's raise was from $10-12K
to $16K, but can't find that information anymore. But one thing that seems clear is Kramer got a raise big enough that Ringo was comfortatble asking for $25,000.