pin driver difference between early/later VIC-II?

Hi all,
some time ago I've restored a C64 Rev. A board, NTSC. The one that
didn't even have a heatsink on the internal 7805 regulator (That I had
to add anyway).
The board did still have the original R10 at 300 ohms, so the picture
looked quite dark. Also the board has a 6567R56A and with the old
(wrong according to the schematic) R10 showed a rather noticeable
"chroma bleeding" from left to right, like the chroma signal was
lagging behind the luma signal. This chroma "defect" disappeared
entirely by using a 6567R8.
Changing R10 to 120 ohms gave a quite normal "bright" image and also
the chroma lagging effect
of the 6567R56A appears reduced but still noticeable.
Since I don't have any other NTSC (newer) board nor any other 6567
chip, I wanted to know if my
particular R56A is defective or if there's a reason for this effect,
maybe different driver stage on the output pins?
It's hard to understand what's exactly going on with an oscilloscope.
Any hint is appreciated.

Frank IZ8DWF