Codes in Flugbuchs and elsewhere.....

[cbe2009]

Hello,
I have in my Flugbuchs fairly often come across different type of planes with the D-XXXX code when I look for the code in "Golden years of Aviation" and compare.
I have had a lot of help from the latter, but wonder why there so often is a different opinion of the type of plane?
For example in "Golden years of Aviation" D-IHOH is said to be a He 60, but in my Flugbuch from Obl. Wilhelm Scheeren the type is an Ar 66 C.

Did the aircrew not write their own Flugbuchs or why could a mistake happen so relatively often?
Sorry this long text.

Cheers
Christian