Back many decades ago when I first became interested in wine--I confess: in the 1960's it was Gallo Hearty Burgundy, Cribari Family Jug Red and Almaden Mountain Red; there, I said it--the bottles always listed alcohol content in round figures with no decimals. I did not really care much then. Now it is 13.7%, 14.6%, etc. Also, I recall being told that in California, while there were laws that governed this labeling, there was a liberal leeway allowed in alcohol labeling and European imports were even less trustworthy. What is the case today (now that I might really care).
Both the US and EU allow leeway between what is on the label and the actual abv. Makes sense because often labels are printed before the wine is finished. The variance in the us is 1.5 percentage points, i.e a wine labelled 12.5%abv could be anything between 11 and 14%.
In the EU for reasons that I cannot comprehend it is illegal to show abv as anything other than a full number or .5, i.e. the two abv you mention in your post are illegal on EU labels. Similar variance is allowed.
I don't think abv levels on EU labels are anymore untrustworthy than US labels, just that its a bit more obvious that its rarely exact.
For several reasons, alcohol taxes being the most common, there is an incentive to understate the abv.
I recall a lunch in the south of France where the grower announced the wine were drinking was just over 16%. I looked at the label on the bottle destined for the US and it read 14%. He just grinned and said they don't check.
The ABVs for most of the 1960s California wines I've had had decimal points. They were all higher-end wines.
In recent years I've seen a few bottles with two decimal points on the ABV.