The Italian-English dictionaries undoubtedly translate al riguardo di as "about (smth.)", "regarding smth." (for example, here and here). A short search on Google brings more than 1 mln. cases with the same meaning.
However, the Treccani dictionary gives only one example of usage for a/al riguardo:
a riguardo di, al riguardo di, in paragone di, rispetto a: la luna è molto piccola a riguardo della terra
The same description and examples are given in Voci e maniere di dire italiane additate a'futuri vocabolaristi by Giovanni Gheradini (p.507):
A riguardo di o Al riguardo di. Si usa col valore A paragone di, a proporzione di.
On the other hand, Dizionario fondamentale della lingua italiana by Giacomo Devoto and Gian Carlo Oli says:
A riguardo di, in riguardo di, nei riguardi di, loc. prep. con il valore di 'per quel che concerne' [...], oppure di 'a paragone di' [...].
(no mention of al riguardo at all)
This discussion shows that if you ask five different people, you'll hear six different opinions. Though, at the end of the day, they seem to agree that al riguardo is equivalent to a tale riguardo and means "a questo proposito", while a riguardo di keeps the meaning "in paragone di, rispetto a."
TL;DR There are contradictory entries in several dictionaries. Thus, I'm looking for an authoritative opinion on:
- whether both a riguardo di and al riguardo di still have the same meaning of "in comparison with", and/or
- whether the meaning of one or both of these phrases has changed over years (when? how?), so that a riguardo di is now out of use, while al riguardo di attained the meaning "with regard to."
Could anybody help me to clarify it? Confirm any of these claims, have some evidence, grammar rules, something to rely on?
