Abbreviations vs. contractions. Do they differ in pronunciation or only in spelling?

Question

Lexico and Imperial College London say that the difference between abbreviations and contractions is that contractions omit letters in the middle and not in the end, hence Dr, for example, is a contraction and not an abbreviation.

Lexico:

Contractions are a type of abbreviation in which letters from the middle of the word are omitted. Examples include: Dr (Doctor), St (Saint), Ltd (Limited), Revd (Reverend).

Imperial College London:

An abbreviation omits letters from the end of a word and a contraction omits letters from the middle of a word. <...> Contracted titles such as Dr, Mr and Mrs should not be followed by a full stop.

Larry Trask in his article on the website of University of Sussex, on the other hand, have another view, and considers Dr to be an abbreviation and not a contraction:

Abbreviations must be clearly distinguished from contractions. The key difference is that an abbreviation does not normally have a distinctive pronunciation of its own. So, for example, the abbreviation Dr is pronounced just like Doctor, the abbreviation oz is pronounced just like ounce(s) and the abbreviation e.g. is pronounced just like for example. (True, there are a few people who actually say "ee-jee" for the last one, but this practice is decidedly unusual.) A contraction, in contrast, does have its own distinctive pronunciation: for example, the contraction can't is pronounced differently from cannot, and the contraction she's is pronounced differently from she is or she has.

Answer 1

The answer is yes. They do differ in pronunciation and in spelling. As a general rule, contractions are pronounced as if letters are not omitted. Abbreviations pronounced as they are written.

Examples might be in America, UCLA for the University of California, Los Angeles. Abbreviated, it is pronounced U.C.L.A. Some abbreviations have become acronyms. Militaries, Space Agencies, and businesses, etc., tend to be prolific in turning titles for organizations, then churning out abbreviations for them, then making those abbreviations into acronyms that are phonetically sounded out. Then again, sports such as Cricket, basketball, golf, soccer, as well as professions all do it, too.

Example: North Atlantic Treaty Organization was abbreviated to NATO (N.A.T.O.) which is phonetically read out as North Atlantic Treaty Organization; but, turned that into an acronym, NATO (phonetically pronounced as "naytou.") There are many examples where abbreviations become acronyms.

In American English grammar, abbreviations for titles, such as Doctor, Reverend, etc., require a period or dot, or full stop. (Dr.). In British English, they expressly do not.

My best advice is to pick one authoritative source--and stick to it. For British English, I'd choose Oxford; but, many side with Cambridge. Pick one. If in America, Websters or American Heritage. The point is, if you can have four watches, you never know what time it is. If you have to have four watches, know one is for New York, another for London, yet another for Tokyo, and the last for Hawaii. With one, however, that's exactly what time it is.