Or in your case an owners manual for the Japanese market, you can find the information that suits you.
The wide range of acceptable oil weights suggests that engines are not as particular about the oil as some people believe. For your engine 0W20 can be used year around in the U.S.
0W30, 5W30 and 5W40 can be used in other markets, seems like most common oil weights are acceptable.
I always like to further my knowledge not just accept what some one tells me or believe everything you read on the internet see on tv ect. If I didnāt I would be putting 20w50 in my car because I got a bad motor lol. Same reason would you waste 91 octane gas in a 85 Ford tempo? Lol that is if it actually still ran now lol. No you would put in 89. But dosent 91 burn cleaner and get better mpg. Nope but thatās what everyone has been spoon fed. But really for the most part you are correct. The OM is a guide line that is what the manufacturer suggests. If not it would be the same for every car every envoirment every case.
Iām not sure if you completely āget itā . . . or perhaps the comparison could have been worded a little differently
No offense intended
Filling up your 1985 Ford Tempo with 91 octane will harm nothing except your wallet
But filling the crankcase of a modern dohc dual variable valve timing motor with 20w50 might harm more than your wallet. It might actually harm the motor, not immediately, but I would expect some negative consequences to occur. The viscosity would be all wrong. Some of the engineers on this forum can better explain why damage could/would occur
Thanks for the detailed confirmation.
None of my cars automatically call for it, and I wasnāt interested enough to look for its possible optional use in any of my ownerās manuals. So I went with the question and a hope to avoid confrontation.
My 1974 Triumph TR-6 owners manual specs 20W-50 whenever the temperature is over 14 degrees Fahrenheit
40w is ok for race use with high oil temps. a 94 chevy truck with worn bearings is a different case
Your engine would be fine with 20w50, as you say
I was talking about using 20w50 in a modern engine . . . dohc dual variable valve timing, for example . . . that would not be a wise decision, in my opinion
Even some modern engines spec heavier-than-you-might-expect oil. For example the E46 M3ās specād a 10W-60 oil. The 2012/2013 Mustang Boss 302 specād a 5W-50 weight oil. Weirdly, the Track Pack equipped 2012-2013 Mustang GT also specified 5W-50 while the cars without the Track Pack specified the typical 5W-20. The strange thing is that there are no differences in the engine with track pack cars vs. the non-track pack cars.
Thank you for pointing that out 
The difference between the track pack cars and the non track pack cars is the way they are expected to be driven. Notice that the extreme performance cars vs milder versions of the same cars vary more in the second number than the first. That is because the first number is the base oil and te second number is achieved with viscosity index improvers.
Contrary to popular belief even a 0w40 oil does not thicken as it warms, it just thins less. in other words a 40 weight oil is thinner at operating temps than a 0 weight oil that is cold. That is why the first number is the more important one for VVT.