Wow. I wish I had taken pics of the valve cover of my 42 year old, 8300 hour Farmall tractor when I adjusted the valves. It barely had any varnish, let alone sludge, and it sits most of the time. It get three year oil changes (verified by UOA) and based on some things I found when I got the tractor seven years ago, such as a hydraulic oil filter with 1980s date codes, the oil changes in it's past may not have been even that frequent.
Posting that undocumented, unattributed pic as some kind of evidence is disingenuous. Doesn't prove a dang thing.
Take it to the bank, in most conditions, the oil can barely tell the passage of time.
Before you newbs start arguing with me, go back and search this topic or go back and read some of my older posts on long OCIs, with UOA documentation. It will connect you with a whole lot of data (from me and many others) and not old wive's tales. We had some very long and fruitful discussions on this in the past and there has been a lot of great info posted. It's well worth the time to search it out. I regularly do 18 month to two year OCIs on a Honda and Ford truck (with UOAs) as well as two and three year OCIs on various farm equipment and small engines. There are a number of others here with similar setups.
VR1: A friendly word of advice. Don't bring up the Pennzoil/Sludge thing again without your best flame suit on. The first time gets you laughed at... a grace period. After that... whoosh... your hair and eyebrows are gone. ( : < ).