This is what my 628A is showing on CLKOUT. It is a well used PIC date coded 2009 running from 5.05V VDD at 19C.
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The frequency implies 3.994MHz internal clock which is an error of only about 0.57%
There is quite a lot of jitter on the clock, hence the high deviation figure which is quite noticeable if I beat CLKOUT against my local AM radio station on 990KHz but it confirms the central frequency is accurate.
The program doesn't change CLKOUT but using it as a way of assessing the speed is unreliable of course.
Brian.